Signal quantization levels can have significant impact on the performance of a GPS receiver, especially in the present of the interference. In this paper, signal quantization model for estimating interference suppression of the correlator output and evaluating the performance of GPS receiver is presented. With the proposed model, performance of the receiver in acquisition process is demonstrated by showing the quantization effects on SNR degradation and detection. Test results show the limits of the low-SNR acquisition of the receiver and the better performance GPS receiver will achieve with a proper set quantization method.