Combining inertial navigation principles with signal processing, this paper first proposes a simplified but efficient mathematical model of INS-assisted second-order tracking loops so as to analyze the tracking capability. Secondly, the optimal bandwidth of INS-assisted Phase Lock Loop (PLL) is proposed to remove the period-amplitude outcome caused by Schuler frequency, and thus to ensure the absolutely satisfactory tracking capability. By theoretical simulation, the INS-assisted tracking ability superior to the receiver without aiding is quantized according to different grades of INS, and the optimal bandwidth is evaluated. The results verify the availability.