An apparatus and a method for assembling optical module. The apparatus includes: a plurality of fixtures, an alignment mechanism, a power supply, a spectroscopic prism with a light incident surface close to the plurality of optical modules to be aligned, a first image collecting means close to a first light emitting surface of the spectroscopic prism and a second image collecting means with a second light emitting surface of the spectroscopic prism; the controller is configured to determine a light spot that does not meet a quality requirement according to the positions and/or sizes of the plurality of imaging light spots, and generate a corresponding aligning instruction, and determine a to-be-assembled lens corresponding to the light spot that does not meet requirements according to a correspondence between a to-be-assembled lens and the light spot, and output the aligning instruction to an alignment mechanism to adjust a position of the lens.