In order to find a carrier-to-noise ratio estimation method with low computation and strong practicality, this paper draws on the experience of the classical variance summing method and proposes an improved algorithm. The distribution of the absolute value of the I-branch accumulative value is deduced when stably tracking GPS signals, and an expression for estimating the carrier-to-noise ratio is given based on its statistical characteristics. The Q-branch accumulative value is not necessary in this algorithm. From the aspects of estimation accuracy and computation, the improved algorithm is verified by simulation and actual measurement data analysis. The results show that the overall performance of the improved algorithm is equivalent, with an error of less than 0.4 dBHz, the stability is better than that of the classical variance summing method and narrow to wide power ratio method, and the computation is reduced by 50% compared to that the classical algorithm. The method has certain practicality in some receivers with limited hardware resources.