Abstract: Current GPS receiver search strategies are based on the sequential search of the C/A code phase and carrier frequency.Based on the two-dimensional sequential search,the probability density functions of detecting signal and undetecting signal are deduced with different numbers of accumulation.A novel acquisition algorithm using adaptive threshold is presented,which can automatically change the threshold according to different satellite signal power and keep the probability of false acquisition invariable.This algorithm is faster than the traditional algorithm using fixed threshold,thus the time to the first fix is reduced.