As the accuracy requirements of optical instruments continue to increase, optomechanical design engineers increase the dimensional tolerance requirements of key components when designing the structure, which puts high requirements on the difficulty of processing, and the cost increases accordingly. Therefore, it is a problem that needs to be solved they are meeting the accuracy requirements of optical instruments, in precision instrument engineering to reduce the processing difficulty and cost at the same time. The pointing accuracy during the derotation process is determined by the error coupling between multiple components, and the imperfect mechanical rotation, internal imperfections, and structural deformation during the rotation will cause pointing errors. Taking the K-mirror derotation system equipped with optical astronomical telescopes as an example, in view of the coupling of multiple error sources in the optical-mechanical structure, the error distribution requirements of the optical-mechanical components are strict. The Monte Carlo algorithm is used to decompose the coupling of multiple error sources. At the same time, a particle swarm optimization algorithm is proposed to perform intelligent error distribution on multiple error sources to guide the optimization of tolerance distribution, optimal design and structural parameters of machined parts in the process of optical-mechanical structure engineering. First, according to the working principle of the K mirror derotation system, combined with the K mirror derotation pointing accuracy caused by the optical-mechanical structure, the error source is analyzed, and the mathematical model of the derotation system pointing accuracy is built, in which the rotation figure on the focal plane after derotation decided to determine the derotation pointing accuracy. Find out the error source that affects the pointing accuracy of the derotation, including the matching size of key components and the selection of standard parts. According to the working principle of the retraction system and the design scheme of the optical-mechanical structure, the main factors affecting the directionality of the K mirror retraction system are the relative poses of KM1, KM2, KM3 and the deviation angle between the mechanical rotation axis and the main optical axis of the K mirror assembly. Then the error decoupling is carried out through the Monte Carlo algorithm, the pointing accuracy is the optimization goal, the sensitivity of the error source is the main optimization path judgment factor, and the processing difficulty and cost are the secondary optimization path judgment factors, to establish the optimization model. The quasi-particle swarm optimization method is used for the error source of intelligent allocation. There are multiple permutation and combination methods for the results of the particle swarm optimization, which considers the value of multiple factors such as small offset, low processing cost, and less adjustment required. Through optimization iterations, an allocation plan that meets the accuracy of the instrument while reducing cost and processing difficulty is obtained, and guides the optimization design, selection and processing tolerance allocation of key components in the K-mirror structure design. Finally, the optical-mechanical coupling simulation analysis method and the experimental setup method are used to analyze the derotation pointing accuracy of the designed K mirror derotation system. Among them, the simulation analysis method uses MATLAB to establish a unified simulation model, connects the finite element simulation software of the optical-mechanical structure and the ray tracing software to perform the optical-mechanical coupling analysis, and the anti-rotation pointing accuracy obtained is 6.95''. In the experimental setup method, when the adjustment is optimal, the graph displayed on the detector is intercepted, and the smallest circumscribed circle of the graph is found, and the best anti-rotation pointing accuracy is 14.24''. The feasibility of the optical-mechanical structure design scheme of the derotation system and the intelligent error distribution scheme of the optical-mechanical system is verified.