In view of requirements that intrinsic safety power supply must has multi-protection of over-current and over-voltage, the paper introduced working principle of a circuit of mine-used intrinsic safety power supply based on LM317 regulator, analyzed design requirements of fuse, filter capacitor and regulator in the circuit, and detailedly introduced calculating method of parameters of circuit of over-current and short-circuit protection and circuit of over-voltage protection. The design of double protection of over-current and over-voltage in the circuit of the power supply provides reference for designing reasonable and reliable intrinsic safety power supply.