Kenneth Dymond, 37, also made contact with a 15-year-old girl over the internet.
Lincoln Crown Court heard that more than 500 images were recovered from Dymond's computers and phones after a raid on his home in August 2015.
He was also placed on the sex offenders' register for 10 years.
More on this and other Lincolnshire stories.
Dymond of Magna Mile, Ludford, Lincolnshire, was serving as an detective constable in the Met's Specialist Crime and Operations Command at the time of the offences.
Stephen Kemp, prosecuting told the court that the internet search history on Dymond's computers "identified various terms which indicated searches for material of a paedophilic nature".
Mr Kemp added: "There were extracts of a Skype conversation recovered from a laptop which appeared to be from a 15-year-old girl's brother calling the defendant a paedophile.
"That person threatened he would go to the police if the defendant did not delete his sister's profile."
Reka Hollos, defending, said Dymond suffered from chronic depression and had undergone counselling for his addiction to pornography.
"He is very remorseful for what he has done," she said.
Judge Michael Heath, passing sentence, told him: "As a serving police officer you ought to know that children are grievously abused so that this material, this utter filth, can be put out there on the internet for people to view it.
"I cannot suspend the sentence in a case such as this."

The Daggers, who reached League One in 2010, needed victory to keep their slim survival hopes alive.
Goals from Jamie Cureton and Clevid Dikamona gave them hope after Jay Simpson fired the O's into a 2-0 lead.
But Armand Gnanduillet fired in the winner to relegate Dagenham and keep Orient's play-off hopes alive.
Dagenham reached the Football League for the first time in their history in 2007, but they now return to the National League under John Still, the same manager who took the club from the Conference to League One.
The Daggers have League Two's worst goal difference, and have conceded 20 goals more this season than they had at this point last term.
Still's side have also struggled in attack, with 40-year-old striker Jamie Cureton netting nine goals, compared to the 20 he scored as Dagenham finished 14th in the 2014-15 campaign.
Boss Still, who returned for his third spell at the club in December, told BBC Radio London on Wednesday that he is committed to helping the Daggers gain promotion from the National League next season.
Victory leaves Orient two points adrift of the play-off spots and comes four days after player-manager Kevin Nolan was removed from his managerial role.
Leyton Orient interim manager Andy Hessenthaler told BBC Radio London:
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"For me to lose two managers this season has been very tough and I've found it very hard this week.
"We had to be professional, we're here to do a job and if I wasn't professional then I wouldn't be true to myself.
"We owe it to the fans. At the end of the day there's nobody bigger than the football club - the fans are the biggest part of the football club.
"We made it a little bit nervy because we gave two sloppy goals away, but in the end that's what we need to do now - we need to win games if we're going to get into the play-offs."
Dagenham & Redbridge manager John Still told BBC Radio London:
"I think for half an hour in the first half we lacked organisation and lacked discipline.
"If you haven't got organisation and you haven't got the discipline to play 90 minutes, the outcome is inevitable.
"Dagenham over the years are going to get beat, it's responding to that that the club's not been able to do this year."
A detective serving with the Metropolitan Police has been jailed after admitting downloading hundreds of pornographic images of children.
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Dagenham & Redbridge have been relegated from League Two after losing at Leyton Orient, ending their nine-year stay in the Football League.