Millimeter wave radar has become one of the most important sensors for advanced driving assistance systems (ADAS). Although it has strong environmental adaptability because of its unique frequency band, its performance is still largely affected by environmental noise, which may cause Radar False Detection, Misdetection, Inaccurate measurement on distance, velocity and incident angle, and so on. While field experiment is traditionally a necessary means to investigate the mechanism on radar detection and noise disturbance, it is difficult, sometimes impossible, to perform in-vehicle and filed testing due to the time, cost, flexibility and safety in setting up driving scenarios that can hardly cover a wide range of variations, uncertainties and complexities. Therefore, it is important to model radar signals to reflect its physical nature by deeply understanding its mechanism. The research presented in this paper is based on the development of millimeter wave radar virtual test simulation platform. In this paper, we discuss the problem of "the mechanism analysis and simulation of radar environmental noise”, summarize and outline the source and mechanism of the radar noise, and present a set of environmental noise mechanism modeling and simulation scheme for Automobile Millimeter Wave radar. The paper can provide more realistic radar noise simulation data for the simulation of ADAS radar. Firstly, the purpose and significance of the research of radar vehicle noise are described, and then, we analyze the traditional radar noise sources and generating mechanism, at the same time, the mechanism of radar noise modeling method of home and abroad are discussed; After that, the limitations of the application of the existing noise modeling methods in the simulation of automotive radar noise are analyzed; On the basis of the above discussion, the paper studies three aspects in detail, Firstly, the mechanism of the false detection ,such as "multi path propagation of electromagnetic wave" and "multi radar interference", is studied; Secondly, we study the mechanism of the missing detection, such as "environmental attenuation" and "noise variance threshold fluctuation"; Finally, the simulation of the noise mechanism is carried out, And the measured results of Delphi radar are collected, the accuracy and the difference between the simulation data and the real date in the target false detection and missing detection, are compared and analyzed, and we draw the contrast curve. Compared with the simulation results, it can be concluded that the "noise" mechanism and the simulation scheme proposed in this paper is in line with the actual work of the radar, the conclusion of this paper has a great contribution to the ADAS virtual test based on millimeter wave radar.