According to the condition that the operating performance of the traditional GNSS receiver is not ideal in the weak signal environment，firstly the article analyzes the working principle of traditional receiver and vector receiver, summarizes the traditional receiver's performance deficiency in the weak signal environment，secondly the tracking performance of the traditional scalar receiver and that of the vector receiver are compared in the weak signal environment, and simultaneously the method of setting up the delay interval of double-code is put forward to optimize the vector tracking performance. The technology of vector tracking is used to make up for the defect of traditional receiver in the weak signal. The experimental results show that the double-code delay interval vector receiver which uses EKF algorithm is superior to the traditional scalar receiver in tracking performance in the condition that the carrier-to-noise ratio is 15-22 dB/Hz, and its' tracking error is about 20 ns smaller than the tracking error of the one-code delay interval vector receiver.