The invention discloses a direct current system insulation detection method based on a resonance compensation theory. An inductance branch circuit with an ammeter is switched through a bus so that a capacitor-to-earth in a direct system is compensated; a resistance branch circuit with an ammeter is rapidly switched with high frequency through a single-chip microcomputer so that the voltage and current frequency in lines can be changed; and an auxiliary inductor and the capacitor-to-earth generate resonance so that the influence on insulation detection by the capacitor is eliminated. In essence, harmonic waves are not injected to the circuit so that the direct current system is not affected; by employing an alternating current sensor with high precision and a rapid switching circuit, direct current voltage and current waveforms in the circuit are changed and converted to square wave alternating current; and the resonance compensation theory and a high-speed switching resistance changing waveform method are combined for high-precision fault current measurement, the resistance-to-earth is calculated, and the insulation detection precision of the direct current system is improved.