The invention provides a microfluidic in-situ liquid environment measurement system based on an ellipsometer as well as a measurement method and application of the system. The system comprises the ellipsometer, a microfluidic chip, a micro-injection pump, an electric displacement platform and a control unit, wherein the microfluidic chip is fixed on the electric displacement platform; the electric displacement platform is arranged on a sample table of the ellipsometer and is connected with the control unit; the micro-injection pump is connected with the microfluidic chip and the control unit respectively. According to the microfluidic in-situ liquid environment measurement system based on the ellipsometer, the ellipsometer can be used for measuring the optical parameters of a sample with a flowing state in a liquid sample pool, and the liquid environment and the growth situation of microfluidic material can be measured in real time, so that the demand of optical constant measurement of the ellipsometer in the liquid environment can be met; furthermore, the optical constant measurement method of the system is simple, easy to operate, high in degree of automation, convenient and fast.