Through many studies on the changes of the amplitude and the spectrum of microtremors in the period of cold air process in the digital broadband date from Gaotai. We also researches on the process of cold air disturbance to the microtremors in time-domain and frequency-domain. Then we discovered that in the process of cold air, the microtremors curve will be a big periodic perturbation or jitter distortion. the process with the cold air from start to finish, the 0.001~0.005 Hz amplitude-frequency value changed greatly,and the process had the characteristic of rapid increase-reach to maximum-dicrease then return to the normal, and the maximum disturbance data will happen at the time of maximum temperature decrease.