In high-precision fiber-optic gyroscope (FOG) system, the spike noise of DC-DC power source can lead to a considerable disturbance to the signal processing circuit of FOG, which results in a sampling error. In this work, the cause of spike noise and the influence mechanism were clarified. The slew rate control technology was researched and proved to be an effective solution to prevent spike noise of FOG power source. Using slew rate control technology, a kind of low-noise power module has been developed and applied successfully in the FOG system. This power module consists of DC-DC circuit and LDO circuit, and slew rate control circuit was used in the DC-DC circuit to realize low-noise performance. The peak-to-peak noise value of the developed power module was tested to be about 1 mV in a bandwidth of 200 MHz. Two typical FOG systems were tested with the use of this lownoise power source, and their output noise improvement were 3.1% and 4.4%.