The invention provides a detection method and system for LTE downlink PSS. The CP type and initial time deviation of OFDM symbols are estimated via the least square error criterion; and according to the estimation result, local optimized search of a small sliding window is carried out every an OFDM symbol length till subframe. A global optimized search algorithm in which PSS detection and calculation are carried out each time a time-domain sample value is received in subframe time in the prior art is decomposed into multiple local optimized search, the calculation amount of PSS detection is greatly reduced, the PSS can be detected rapidly and accurately, and the performance of LTE downlink synchronization is improved.