Abstract: This paper analyzes the principle and process of discharge in complex intrinsically safe circuit, gets the general form of mixed intrinsically safe circuit, obtains the calculation model of discharge voltage, discharge current and discharge power under capacitive discharge condition of resonant circuit by mathematical analysis, and analyzes the influence of circuit parameters of discharge current and discharge power factor. The results show that the discharge energy mainly comes from the spark circuit of the energy storage element, the effect of supply voltage on the discharge current, discharge voltage and discharge power can be ignored; with the increase of the capacity of the capacitor, the discharge current rise rate and the maximum value increase rapidly, the discharge power increases too; with the increase of inductance, the rising trend of discharge current slows down, the maximum value of discharge current decreases, and the discharge power decreases.