The field-to-voltage transfer coefficient (∂ B/∂ V) is an important parameter of the multi-channel superconducting quantum interference device (SQUID) magnetic detecting system. The SQUID devices and the readout circuits have the inevitable differences among different channels, so the accurate calibration of system channels is rather significant. In this paper, We first used the circular PCB coils for 36-channel MCG system calibration, and the other one is based on a traditional method in which a uniform field is produced by square Helmholtz coil. The calibration data show that the results are basically the same. The calibrated ∂ B/∂ V values using circular PCB coils are in a range from 1.46-1.73 pT·mV-1. And those of square Helmholtz coils are mostly within a range from 1.56-1.64 pT·mV-1.