Based on the principle of micro-scale discharge, the micro-nano ionization gas sensor has the characteristics of fast response, high precision and easy integration. It is expected to achieve rapid and accurate detection of gas. At present, there is a lack of systematic analysis of the inter-polar discharge process of the new sensor. This paper uses the fluid-chemical dynamics methodology to create a 2D space discharge model of the N₂-O₂ mixed gas at the micron gap and the nano-tip field in ambient atmosphere at normal temperature and pressure. Meanwhile, by analyzing the mutual coupling between the space electron transport process, the discharge current density, and the space electric field strength, the paper clarifies the dynamics of space discharge in the field, improves how internal discharges work in such micro-nano structured ionization gas sensors, and analyzes the pattern of influence of different polar distances on space discharges. The results show that the electric field in the space remains constant as the production and consumption of positive and negative ions reaches a dynamic equilibrium in the field. It is reflected in the field strengthening effect of positive ion groups to the cathode plate and of negative ion groups to the anode plate, as well as in the field weakening effect between positive and negative ion groups. The resulting stable and strong electric field of the cathode makes sure that space discharge is maintained, and the discharge current density stabilizes. Initially, as the polar distance decreases gradually, the electric field strength between the poles and plates increases. It plays a leading role in the accumulation of electron energy and in the increase in the number density of electrons, thus leading to the increase of the output current density up to the peak value when the polar distance D = 50 μm. As the polar distance decreases, the field strength between the poles and plates increases. Despite that, when electrons accumulate energy up to such a level that gas molecules can be ionized, the necessary movement distance and the distance required to increase the number density of electrons decreases. As a result, the degree of ionization weakens, and the field strengthening effect of positive ions decreases. In other words, the increment of the field strength caused by positive ions at the tip decreases, and in turn, the discharge current density decreases. This pattern serves as a theoretical support in the optimization of the micro-nano structured ionization gas sensors.