the theoretical limits of watermark spread spectrum sequence at present the spread spectrum ss sequences used in watermark include iid random sequences and the sequences used in ss communications they appear earlier than digital watermark almost no researchers pay attention to whether they are really fit for watermark in this paper we compare the ss watermark channel and the traditional ss communication channel we find out that their correlation property is different considering cropping and translation attacks we define watermark auto and crosscorrelation and propose loose autocorrelation and tight crosscorrelation lactcc properties for ss watermark the lactcc properties are that whether or not synchronized the autocorrelation is equal or close to 1 and the crosscorrelation is equal or close to 0 accordingly the peak correlation is divided into the peak autocorrelation ra l and the peak crosscorrelation rc l we establish the lower bound of r c l and the higher bound of ra l respectively the two bounds indicate that no matter how small the cover is reserved the extractor can always find a threshold to distinguish auto and crosscorrelation in theory