Taking a 1m aperture photoelectric theodolite as study object, its key components including four-way, turntable and base are structural optimized so as to improve structural rigidity while reducing structural mass. First, various components’ working characteristics and relationships with the other parts are studied, based on these, reasonable finite element model of these components are established, then each component’s optimal material topology are obtained by continuum topology optimization. According to structural topology, lightweight truss structure models are constructed and the models’ key parameters are optimized in size. Finally, the structures optimized are verified by finite element analysis. Analysis prove that comparing to traditional structure, lightweight structures of theodolite’s three key components can reduce mass up to 1095.2kg, and increase ratio of stiffness to mass. Meanwhile, for other indexes such as maximum stress, static deformation and first-order natural frequency, lightweight structures also have better performance than traditional structure. After alignment, angular shaking error of theodolite’s horizontal axis is tested by autocollimator, the results are: maximum error is υ =1.82″, mean square error is σ =0.62″. Further, angular shaking error of theodolite’s vertical axis is tested by 0.2″ gradienter, the results are: maximum error is υ =1.97″, mean square error is σ =0.706″. The results of all these analysis and tests fully prove that the optimized lightweight key components of this 1m aperture theodolite are reasonable and effective to satisfy this instrument’s requirements.