In order to solve the issue of low utilization of light and low-precision reconstruction in the existing coded aperture snapshot spectral imager (CASSI), the computational spectrometry characteristic of high utilization of light and precision is developed through the research on CASSI. Compared with CASSI, sample of the full-color branch is added, which is complementary to the CASSI branch in data. Imaging experiment results show the underdetermined degree of reconstruction decreases sharply. By the data alignment and fusion between the full-color branch and CASSI branch, the high-precision data reconstruction is finished. As compared with CASSI, utilization of the optical throughput in the developed system is doubled.