A improved double-beam structure in spectrophotometer was proposed which has an extra calibration light source in the design of the double-beam to calibrate both the main beam and the auxiliary beam in real time. The related optimisation spectral data sampling algorithm was presented to modify the change of sensor response efficiency caused by temperature change, the effect of the proposed structure with a series of customised experiments at at different ambient temperatures was evaluated. Experiment results show that when operated in an environment with a temperature change from 10℃ to 30℃, double-beam correction instrument is able to produce measurements repeatability, the standard deviation with an average is less than or equal to 0.03, and the maximum is less than or equal to 0.04, which is a significant improvement to existing products.