Optical tweezers are unique tools for studying biophysical properties of single molecules. Design and construction of optical tweezers are very important. The optical path, the radial manipulation equation and axial manipulation equation of optical tweezers based on a finite conjugate microscope system are calculated using matrix optics. The influences of axial position adjustment of the objective, the installation location error of the coupling lens, the installation location error of the laser beam control system, and the installation location error of the confocal system lens' on radial trap position manipulation accuracy and axial trap position manipulation accuracy are analyzed. The results show that axial position adjustment of objective introduces no error in radial and axial trap position manipulation. The misalignment of laser beam control system has no effect on the radial manipulation, nor on axial manipulation when the coupling lens maintains alignment. It is concluded that misalignment of components of optical tweezers based on a finite conjugate microscope system has a greater effect on trap position manipulation error than misalignment of components of optical tweezers based on a infinite conjugate microscope system. The radial trap position manipulation error is less than 5.9% and the axial trap position manipulation error is less than 11.4% when the coupling lens installation location error is less than 10 mm. It is shown that optical tweezers can be modified from a finite conjugate microscope system. The formulations provide the basis for theoretical analysis of experimental alignment and adjustment.