Starting from vector refraction theorem, the design principle of transmitted laser beam through double-prism to perform microradian deviation is researched, and the testing problem of fine pointing and tracking in inter-satellite optical communications is solved. The accurate formula for laser beam deviation through a pair of orthogonal prisms is derived, the visual field defined as level field angle and vertical field angle is proposed, and the general situation of laser beam deviation through single prism is also presented. The main parameters of prisms, according to design object and calculation result, are confirmed, and then the numerical simulation on the deviation result of laser beam is carried out. The final results from the tests accord well with those from the theoretical analysis. The results show, when the prism wedge angle is 4°, the transmitted laser beam changes about 1 μrad as the prism rotates 1′; when the small angle deviation on one side of the minimum deviation angle of each prism is controlled, the scanning range of laser beam in the horizontal and vertical direction is not less than 500 μrad, and the scanning precision of the device is superior to 0.2 μrad.