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There are two difficulties to obtain positioning results in dense urban without auxiliary means. Due to the signal is very weak, receiver can’t obtain positioning results because pseudo-ranges are unavailable. Though the receiver can obtain pseudo-range observations through some senior weak signal processing algorithms, the receiver still can’t achieve the required positioning results. This paper is mainly aiming at the above two problems, and proposed a two- solutions to resolve them. Solutions are as follow: the conventional receiver needs to get 4 or more satellites measurements to give a positioning result, but four satellites measurements is difficult to obtain in dense urban. This paper proposes a solution that as long as the receiver enters into the tracking mode, namely 1 millisecond measurement can be obtained, this receiver can give the positioning results. If the quality of measurements in dense urban is poor, the positioning results become the worse than in the open sky. This paper proposes another solution that using the fault diagnosis principle to improve the position result. The bad measurements can be processed through the non-linear weighting method. In order to verify the efficiency of the above algorithms, the paper processes the actual data.