Abstract: A method to measure milli tesla class magnetic field by coherent population trapping effect is proposed.Using linearly polarized laser to interact with ⁸⁷Rb atoms,two divided CPT resonance signals caused by the nucleus spins in the magnetic field is obtained,and the magnetic induction strength of the magnetic field is derived by analyzing the splitting distance between the two CPT resonance signals.This method can eliminate nonlinear error caused by the high-order term to improve the accuracy of measuring the milli tesla class magnetic field and provides a new scheme for the quantum standard of milli tesla magnetic field.

Key words: Coherent population trapping, Atomic magnetometer, Quantum metrology