A novel fiber Sagnac-like detection system has unique competitive advantages for detecting atomic spin precession in atomic magnetometers. Unfortunately, its operating stability is severely limited by temperature fluctuations. In this paper, we describe a new approach to improve the temperature stability by using the ratio signal as the output instead of the conventional fundamental component. This method can effectively counteract the temperature-caused fluctuations in both light intensity and scale factor of photodetector. For a temperature range from 20°C to 40°C, a relative fluctuation of the ratio output signal of 0.97% was achieved, which was 17.4 times better than the fundamental component output. Moreover, no additional equipment and complex compensation algorithms are required during this process. It is a generic method that can also be applied to improve the stability of other detection schemes used in atomic magnetometers.