Abstract: To address the bottleneck issue that the excessive radial size (>30 mm) of conventional solenoid valves severely restricts the miniaturization of coiled tubing tractors, a highly integrated micro solenoid valve suitable for confined downhole spaces is investigated. Based on the structural principles of solenoid valves, mechanical and kinematic models of the micro solenoid valve were established. The influence of the moving core radius and coil outer diameter on the axial electromagnetic force was quantitatively analyzed using the finite element simulation method, and the optimal miniaturized structural parameters were determined. A prototype of the micro solenoid valve was fabricated, and an experimental system integrated with the coiled tubing tractor was constructed to evaluate the directional switching performance and pressure response. The simulation results show that, under a constant number of ampere-turns, either decreasing the moving core radius or increasing the coil outer diameter effectively enhances the axial electromagnetic force. The optimal parameters were determined as a moving core radius of 3 mm and a coil outer radius of 8.5 mm (resulting in a maximum diameter of 17 mm and a height of 18.23 mm). Under this configuration, the axial electromagnetic force consistently exceeds the motion resistance throughout the stroke. Experimental validation confirms that the micro solenoid valve operates smoothly at a pressure of 3.75 MPa, with a spool opening response time of approximately 52 ms, demonstrating stable and reliable performance. The designed micro solenoid valve achieves a maximum radial size of only 17 mm without compromising driving force, significantly enhancing the integration density of the coiled tubing tractor. The findings provide a theoretical basis and experimental support for the development of miniaturized hydraulic control systems in downhole tools.