As we all know, millimeter wave radar has become one of the most important sensors of advanced driving assistance system (ADAS). However, though millimeter wave radar has strong environmental adaptability because of its unique frequency band, but its application performance is still largely affected by environmental noise, the main problem is that the environmental noise may cause the common problems such as false alarm, missing detection, inaccurate distance measurement, inaccurate velocity measurement, and inaccurate angle measurement, and so on. Therefore, R & D engineers must carry out a large number of repeated tests, it may develop a higher reliability, higher environmental adaptability of millimeter wave radar applications, extract the precise target data, and develop ADAS system more perfect. There are two ways to repeated tests, that is, the actual test and virtual test. It is difficult, sometimes impossible, to carry out the actual test, on the one hand, it is difficult to establish a set of actual driving scenarios that can cover a wide range of variations, uncertainties and complexities; on the other hand, due to the high cost, long duration, poor flexibility, and safety problems. The virtual environment test can avoid the shortcomings mentioned above! 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 noise of Automobile Millimeter Wave Radar, 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 millimeter wave 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 alarm ,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"; Thirdly, the paper studies the mechanism of the inaccurate distance measurement, inaccurate velocity measurement, and inaccurate angle measurement, such as "radar frequency modulation error noise" and "Doppler frequency shift noise"; 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 alarm, missing detection, inaccurate distance measurement, inaccurate velocity measurement, and inaccurate angle measurement, 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!