An optical focusing mechanism for short-arc xenon lamps is designed. The focusing control meth. ods on axial focusing and lateral focusing are designed and calculated respectively. On one hand, axial focusing method is realized by the structure of fine thread. On the other hand, lateral focusing method is realized by a set of eccentric wheels. Three-dimensional and continuous focusing method of the mechanism is realized at last. Based on this, the structure sample of the focusing mechanism is developed. Its reliability is verified by many tests and good results are obtained.