With the deeper research of the vector signal and the extensive use of the vector signal analyzer, and based on the MLS signal’s characteristic, which includes digital signal and analog signal. This essay presents a mathematic relation between EVM (Error vector magnitude), SNR (signal to noise ratio) and phase noise. In the mean time on the basis MLS angle analyses theory, by measuring the phase noise of the carry wave signal and the EVM of dada signal, which is within the dynamic range, we can calculate the SNR of the scan beam accurately and quickly. In this way it’s easy to realize the calibration of angle precision in different output power signal. Through the experiment, it’s a simple and convenient method to calibrate the angle precision of the output signal of MLS simulator.