For the design of the RF frontend without AGC circuit of GNSS receivers with the existence of jamming,when the A/D sampling chip and mixer are fixed,an optimal design method of the linearity is proposed in this paper.And a method to compute the gain,power 1 dB compression point,thirdorder intercept and noise figure of each class of circuits is proposed for the requirement of antijamming,which can be guidance for components selection.Based on this optimal design method,a RF frontend of a GNSS receiver is designed,which achieves the expected effect and demonstrates the effectiveness of the method.