A kind of focusing structure for a space remote sensor was designed, which combined a harmonic drive,a screw, and a line guide rail to compensate the shortcomings of traditional focusing structures. A motor model was selected according to the analysing on a resistance torque,then the resolution of focusing structure was calculated to be 0.43 μm. The structure was tested in a dynamic environment with the whole machine, and focus precisions were compared before and after the dynamic environment testing. The testing data indicate that the line tilt is less than 20″ and the displacement error is less than 5 μm, which meets the requirement for use.Experimental results prove that this focusing structure is characterized by his compact volume, high rigidity and well precision.