Avalanche Photodiode (APD), with its advantages of small size, fast speed, and high sensitivity, stands out from a large number of photoelectric detection devices and is widely used in pulsed laser ranging reception. In the field of engineering practice and academic research, reasonable modeling of APD devices and full closed loop simulation of Constant False Alarm Rate (CFAR)laser ranging receiving circuit using this model can greatly improve system design efficiency, reduce research and development costs, which is of great significance to the performance evaluation of laser ranging receiving system. At present, many institutions at domestic and abroad have established a variety of APD circuit simulation models. Most of these models are based on the carrier rate equation. After proper and reasonable approximation, the APD is equivalent to a three terminal circuit composed entirely of electronic components through mathematical simulation. However, the establishment of these models is based on devices' internal parameters and material properties, involving intellectual property rights, trade secrets and other reasons, which are usually not provided by manufacturers. Therefore, these models are suitable for the research and development process of devices, and not for the full closed loop dynamic simulation of CFAR laser ranging circuit. On the market, APD device manufacturers often only disclose the external characteristics of the device, which makes the existing models difficult to use effectively in the actual scientific research work. Therefore, how to use the limited device parameters to explore new modeling methods, carry out mathematical modeling and circuit packaging for external characteristic parameters, establish the APD circuit simulation model, and realize the full closed loop dynamic simulation of CFAR laser ranging circuit is still a problem to be solved. In this paper, an avalanche tube model based on a nonlinear correlation source is established to solve the above problems, and the full closed loop simulation test of CFAR laser ranging circuit is carried out using this model. Taking the C30950E avalanche tube assembly, a product of EG&G Canada, as an example, the paper first refers to the C30950E data manual, and uses the Curve Fitting toolbox in Matlab to perform curve numerical fitting according to the correlation between avalanche gain, noise (temperature) and bias voltage. Through fitting, the exponential function model of APD input, output and bias voltage control is established; Then, on the basis of this mathematical model, the nonlinear correlation source control in Multisim 14.2 software is used for circuit encapsulation; Finally, the range receiving amplifier circuit with APD constant false alarm bias automatic control and short-range scattering time gain control is designed, and the automatic gain control (AGC) signal is added. The full closed loop circuit of the constant false alarm laser range receiving amplifier circuit is built using the above APD circuit simulation model, and simulation research is carried out for the system detection sensitivity, false alarm rate and other indicators. The simulation results show that the CFAR ranging circuit can automatically capture the optimal avalanche gain operating bias voltage of APD according to the design value of the false alarm rate. Based on the simulation model, the minimum optical power detection of 25nW is realized. The false alarm rate within the measurement range is 0, and the false alarm rate outside the measurement range is about 65 times per hundred milliseconds. The results are close to the actual values. The simulation tests verify the correctness and accuracy of the simulation model. The simulation provides a design optimization approach for the research and development of APD constant false alarm laser ranging receiver circuit, and the overall modeling and simulation ideas are also instructive for the computer-aided analysis and design of other OEIC circuits.