vilian GPS has found wide applications in civilian areas, while spoofing may lead to malfunctioning of it. Spoofing is a serious threat to civil GNSS system, and therefore it's necessary to study how to detect and reject the spoofing signals. Firstly, an anti-spoofing approach to reject undesired signals by using null-steering is presented. Detailed discussion is given to the method's procedure and performance. Then the suppression of spoofing signals and noise signal is studied, and a method to optimize the weight vectors is proposed. Simulation results show that the optimization significantly increases the attenuation of undesired signals. As C/N0 increases, the attenuation approaches -60 dB (which is only -30 dB without optimization). Therefore, the spoofing signal is restrict to enter into the array. Finally, analysis is made to the impact of null-steering on visibility of GPS satellites. The results show that if the satellite is usable when the SNR is reduced by 12 dB, then all the satellite will not be affected.