The distribution characteristics of power frequency magnetic field in substation is an important basis to reflect the operation state of power system. It is necessary to consider the non-invasive characteristics to complete the calculation. The analysis method of auxiliary measurement using micro intelligent sensor is proposed. The power frequency magnetic field distribution characteristics of typical substation are analyzed by finite element method, the power frequency magnetic field model of typical substation is created by ANSYS simulation software, the power frequency magnetic field distribution law is obtained by solving the model, the non-invasive current measurement method of tunnel magnetoresistance is designed by using micro intelligent current sensor, the non-invasive current is calculated, and the auxiliary measurement is completed. The experimental results show that the maximum magnetic induction intensity in four directions of the main transformer chamber is less than 1.6 P T. The distribution of magnetic induction intensity is weak in the East and West, and strong in the South and North; The noninvasive current measurement results at different times are basically the same as the reading results of class 0.2 standard ammeter; Pasted micro intelligent current sensor can accurately sense the distribution characteristics of power frequency magnetic field in substation.