Abstract: With regard to the problem that the rotary sidewall coring device of shale gas wells cannot be lowered to the coring position with its own weight, the operating requirements of the coring device were analyzed, and the resistance to the coring device in the horizontal wells was determined. Then, a new crawling mechanism transmitted by planetary and bevel gears was designed for rotary sidewall coring device. The functional relationships of the positive pressure of the crawling wheel and the extension speed of the supporting arm with each parameter were established. With the extension speed and push-the-bit force of the supporting arm as the multi-objective optimization function, the order of priority of the influencing factors such as the length, rotation angle, and eccentricity of the crawling arm and the length of the supporting arm was determined through the orthogonal tests. Furthermore, the physical dimensions of the crawling arm and supporting arm were optimized. The analysis results demonstrated that the rotation angle of the crawling arm had the greatest influence on the extension speed and push-the-bit force of the supporting arm. When the rotation angle, length, and eccentricity of the crawling arm and the length of the supporting arm were 45°, 150 mm, 8 mm, and 140 mm, respectively, the extension speed and push-the-bit force of the crawling arm were optimal. The optimization of the lengths of the crawling and supporting arms facilitated the decline in the push-the-bit force needed by the supporting arm and the increase in the extension speed of the supporting arm. The crawling mechanism of the rotary sidewall coring device for shale gas wells provides a new driving method for the sidewall coring device.