Abstract: The paper proposed a design scheme of a power supply circuit with high reliability based on BUCK switching power supply chip LM22671 for mine-used intrinsic safety type apparatus, introduced hardware designs and working principle of input surge immunity and intrinsically safe disposal part, soft start circuit and intrinsic safety type BUCK switching power supply circuit in details, and gave methods of optimizing parameters of key components and experimental data. The frequency of the BUCK switching power supply circuit keeps at 500 kHz with no cross frequency and ripple voltage maintains 10 mV simultaneously without sudden increase when the value of inductor is no less than 47 μH. The efficiency of the power supply circuit is no less than 80% at key load points. The maximum short circuit current, the maximum capacitance and the maximum inductance meet intrinsic safety requirements of GB3836.4-2010 with no exception. The power supply circuit has succeeded in intrinsic safety test and surge immunity test of grade I, which verified high reliability of the circuit.