Gain adjustable photodetectors based on avalanche photodiode (APD) are widely used in fields such as laser communication, laser radar and optical fiber sensing. Combining with low-noise broadband transimpedance amplifiers, they achieve high-sensitivity detection by utilizing the avalanche multiplication effect of the internal carriers in APD. To further enhance the gain dynamic range and response bandwidth of the APD detector, the study explored the relationship between the linear multiplication factor of the APD and the dark current to increase the gain factor of the APD. The amplification scheme of a transimpedance amplifier cascading an operational amplifier improved the gain adjustment range while guaranteeing the detector response bandwidth. In addition, a low-noise high-voltage direct current bias circuit module was designed with a ripple voltage of less than or equal to 2.5 mV. Adjusting the voltage enabled the rapid switching of the APD multiplication factor M between 1, 10, 50, 100 and 200. The maximum adjustable APD detector gain reached 74 dB. The bandwidth was 150 MHz, while the minimum noise equivalent power was only 0.02 pW·Hz^-0.5. This low-noise and large-dynamic range technology solution expands the applications of APD photodetectors.