The design, assembly and experiment of the optomechanical system of a compact spaceborne video camera developed for the 20 kg micro-nano optical remote sensing satellite were introduced, and the integrated optimization method was also proposed. The camera was a Cassegrain optical system including two mirrors and one corrector assembly. In order to obtain the best thermal stability, the mirrors were made of silicon carbide. Firstly, based on the task and overall design of 20 kg micro-nano video satellite, the requirements of video camera were proposed; Then, the optical and optomechanical structure system of the video camera were introduced respectively; In order to further improve the lightweight rate, while meeting the requirements of optical performance, the optomechanical integration optimization method was used to the lightweight design. After optimization, the mass of the optomechanical system was only 3.03 kg, the weight of the whole camera was only 4.76 kg, and the 1^st mode was larger than 120 Hz; Finally, the assembly and ground mechanical experiments of the camera were summarized. The results showed that the camera had very dynamic properties and stability.