What is the effect of expansionary fiscal policy in case liquidity trap situation? I've read that liquidity trap means interest rate is at its minimum and increase in real money stock will not lead to fall in interest rate because people will be demanding whatever the amount is being supplied at that minimum interest rate. Now in books they say that in this situation when government expenditure rises leading to a rise in income and hence a rise in money demand would not lead to a change in interest rate.

But according to me when the demand for money goes up it shifts the money demand curve to the right and above. Given the money supply and fixed price, this should lead to a rise in interest rate. 
Same confusion arises when we reduce the real money supply under the liquidity trap situation. Book says that interest rate will not go down when money supply goes up but it says nothing about money supply going down.
If I've understood correctly (it's not entirely clear from the question), you're asking about a policy of fiscal expansion in a depressionary environment, accompanied by a monetary expansion.

It is conceivable that an increase in money supply, coupled with an increase in money demand, would lead to unchanged interest rates, if those two opposing forces balanced out.