In this Letter, a chromatic confocal measurement system with high stability and accuracy is presented to monitor the evaporation of a sessile water droplet. The stability and accuracy of the system are tested by measuring the thickness of a cover glass. To compensate for the measurement error caused by the lensing effect of the sessile water droplet, a spherical cap model is proposed. Together with the parallel plate model, the contact angle of the water droplet can also be obtained. The evaporation process of sessile water droplet under different environment is monitored experimentally in this work, which demonstrates the potential application of chromatic confocal measurement system in the field of experimental fluid dynamics.