According to the optical system characteristics and the structure of a space solar telescope, a foeal plane focusing mechanism isdesigned to save the installation space and ensure the imaging quality. By using worm gear and eam chute groove as transmission parts,the circular motion of the stepping motor is transformed into linear motion in the normal direction of the focal plane. The focus range is 1.5 mm,the overall size is 167 mm×64 mm×94 mm and the mass is 2 kg. Two adjacent self-lubricating silicon nitride rings arearranged between the base back plate and the cam chute. It can increase the preloading foree without affecting the rotation of the camchute, improve the positioning accuracy to a certain extent, and reduce the backlash error. After that, the design scheme, resolution andself-locking eapability of the foeusing mechanism are introdueed in detail, and the error sourees, theoretical positioning accuraey andfinite element model simulation are analyzed. Finally, the positioning accuracy test and vibration test of the focusing mechanism arecarried out. The resultis show that the positioning accuracy is better than ±4.5 μm and the firsl-order mode is 349 Hz, which is hasicallyconsistent with the finite element simulation results. As a result, it has good dynamic stiffness and can effectively avoid resonancephenomenon. The encoder code values of the focusing mechanism are recorded before and after vibration test, which shows well self-loeking performanee. The focusing mechanism has the characteristics of small volume, large stiffness and high precision, which ean wellmeet the working conditions of space solar telescope.