Abstract: Circular dichroism spectrometer is an important instrument for conformational analysis and physicochemical characterization of chiral molecules. However, the long-term use with high intensity would lead to the deterioration of optical components and the reduction of detector sensitivity. By optimizing the optical components of the spectral system to improve the optical transmission efficiency, and upgrading the large area avalanche photodiode detector (LAAPD) with higher quantum efficiency, the signal-to-noise ratio of the instrument was greatly improved. Moreover, the wavelength measurement range has been expanded from 175~900 nm to 175~1150 nm. In addition, it is very important to thoroughly purifying the instrument with nitrogen before lighting the xenon lamp to exclude oxygen from the spectrometer. The active nitrogen monitoring system (ANMS) combing multiple functions: monitor, schedule, flow rate settings, alarms, aux control and etc. can be installed, which can monitor and control the internal nitrogen purge in real time. Through above improvements, not only strengthened the performance of the instrument, but also saved the cost of nitrogen consumption. More importantly, the service life of the spectrometer will be further extended.