This paper firstly analysis the coherent correlation, non-coherent accumulation detector used in weak satellite signal detection mathematically and statistically, and derives its single threshold based on the CFAR (constant false alarm rate). And then the paper improved the detector under the situation of more than one satellite existing with different signal power. Based on this new type of detector, a threshold calculation method is introduced considering the effect of near-far problem in the weak signal detection. Finally the method is verified and compared to the traditional single threshold with simulated data and collected intermediate frequency real data. The results show that this new threshold method can detect signal efficiently with lower false alarm possibility and larger detection possibility.