Abstract: The end-window Geiger-Miller counter (end-window GM counter) is one of the core detectors in the field of radiation detection. End-window GM counter has many advantages such as low cost, high reliability, and strong versatility, especially in being able to measure alpha, beta, and gamma rays simultaneously, and meets various radiation measurement needs. The electric field distribution of the end-window GM counter is one of the important parameters for evaluating its working performance. The paper aims to solve the difficulty in determining core design parameters such as operating voltage and anode/cathode structure, during the development and design process of a new type of end-window GM counter. The international advanced type of end-window GM counter was took as the research object, key simulation input parameters were identified, refined electromagnetic simulation model was established, and the electric field distribution characteristics inside the counter was analyzed. Finally, the influence mechanism and pattern of the core design parameters of the counter on electric field distribution were researched. The simulation results show that parameters such as operating voltage, power supply mode, anode structure, relative position of anode and cathode, and end-window structure all have an impact on the electric field distribution in the counter. The electric field intensity in the bottom area of the counter is higher than that in the top area of the counter, and is relatively highest in the central area at the bottom, the charged particles mainly drift between the reticulated anode and the bottom surface of the counter. The electric field inside the counter is mainly distributed near the anode, which is the main area where particle multiplication effects occur. The peak electric field intensity appears at the edges of each anode ring and increases with the increase anode ring radius. The peak and mean electric field intensity inside the counter increase linearly with the operating voltage, and uniformity of the electric field is not affected. Negative power supply method can improve the dead time of the counter, but the peak and mean electric field intensity inside the counter decrease, and the uniformity deteriorates. The electric field distribution is more sensitive to thickness of the anode. The anode is more suitable to be arranged in bottom of the counter. The conductive coating can further improve working performance of the counter. The paper provides theoretical, methodological and data support for the development, optimization design, and engineering practice of new and advanced end-window GM counter, and has certain guiding significance for the simulation analysis methods of other gas radiation detectors.