The invention discloses a multi-channel fusion and mixed data transmission system and method of a high-speed video circuit. The system comprises a high-speed serial data receiving module, a mixed datasynthesis module and a channel data fusion module; wherein the high-speed serial data receiving module receives multiple paths of serial digital signals sent by a focal plane circuit and performs serial-parallel conversion to obtain multiple paths of parallel digital signals; the mixed data synthesis module receives the multiple paths of parallel digital signals, intercepts effective pixel digitalizing bits of the multiple paths of parallel digital signals, and performs re-encoding to obtain multiple paths of mixed digital signals; and the channel data fusion module receives the multiple paths of mixed digital signals, adds auxiliary data according to a data transmission format, performs sorting and channel fusion to obtain a path of digital signals. By adoption of the multi-channel fusion and mixed data transmission system and method, the error codes in the digital transmission are reduced, the image SNR and the data transmission efficiency are improved, the scale of the circuit is reduced, and the resource utilization ratio is improved.