The invention discloses a spectrum reconstruction method and system based on a multichannel imaging system, which are used for performing spectrum reconstruction according to the camera response values of a training sample to-be-selected set and a to-be-reconstructed sample set acquired by the multichannel imaging system. The method comprises the following steps: selecting training samples with most similar camera response values from the training sample to-be-selected set for each to-be-reconstructed sample in the to-be-reconstructed sample set respectively to obtain an initially-selected sample set; removing identical samples, and constructing a matrix by the spectral reflectivity information of all samples to perform PCA (Principal Component Analysis) analysis; computing the accumulating contribution rate of a characteristic value; screening the samples to obtain a training sample sub-set, performing spectrum reconstruction according to each training sample sub-set for each to-be-reconstructed sample, and selecting one reconstruction result according to a reconstruction error minimum principle for serving as the final spectral reflectivity value of each to-be-reconstructed sample. By adopting the spectrum reconstruction method and system, the chromaticity accuracy and spectrum accuracy of each reconstructed sample can be remarkably increased, and high-fidelity color reproduction can be performed. Meanwhile, the method and the system are easy and convenient to implement, and are suitable for popularization and application.