Due to the weak energy microseismic events and the characteristics of low SNR data, the quick and accurate first arrival pickup has become the key problem. In view of the low efficiency of manual pickup and the low accuracy energy ratio method in picking up first arrival, the authors proposed entropy and mutual information method. Through studying the features of random variables and correlation degree, the authors proposed a first arrival pickup based on energy and mutual information. First, energy ratio algorithm is used to pick a rough arrival time, and then the mutual information algorithm is used to accurately pick up arrival time. According to the test of the model and the analysis of real data in comparison with conventional methods, the authors effectively verify the accuracy and feasibility of the method. The automatic first arrival pickup is achieved accurately and rapidly.