Abstract: The discharge characteristics of intrinsically safe resistive, inductive and capacitive circuits are analyzed. It is pointed out that inductive and capacitive circuits have larger discharge energy and more complex discharge waveforms. The resistive circuits have relatively simple discharge characteristics. The discharge mechanism and mathematical models of the intrinsically safe inductive and capacitive circuits are summarized. The mathematical expressions of different models, such as linear decay model of discharge current, parabolic model of discharge current, static volt-ampere characteristic model, dynamic volt-ampere characteristic model and arc resistance index model, are given. The advantages and disadvantages of the numerical simulation method of macroscopic and microscopic gas discharge are introduced. The macroscopic methods have a small amount of calculation, but it can only simulate the external characteristics of gas discharge. The microscopic methods have a large amount of calculation, but it can accurately simulate the motion characteristics of particles in the discharge process. The microcosmic mechanism of the DC discharge circuit and discharge arc is studied. Under different electrode materials, different electrode distances and different initial electrical parameters, the influence of different surface emission mechanisms such as thermal field emission and field emission on gas discharge is obtained. According to the current research situation, the problems that need to be solved in the discharge research of intrinsically safe DC circuits are put forward. ① The macro experiment-mathematical model has complex expression and a large amount of calculation. Some models have a single scope of application and cannot truly achieve the non-explosive evaluation of intrinsically safe circuits. ② Most of the research on discharge in intrinsically safe circuits is based on IEC spark discharge devices, which affects the discharge of specific circuit parameters. ③ The numerical simulation of discharge arc cannot quantitatively study the arc formation mechanism during the contact breaking process of two electrodes. ④ There are no more convincing research results on the influence of inductance and capacitance of the inductive circuit and capacitive circuit on the characteristics of discharge arc. ⑤ At present, there are few theoretical studies on how to ignite dangerous gases by electric arc due to circuit break arc or short circuit spark.