Traditional liquid level measurement methods have many defects, such as measurement accuracy is not high, measurement is not continuous, non contact measurement is difficult to achieve. By studying the transparent reagent liquid level online detection method, the paper designs a kind of noncontact photoelectric liquid level detection system,The system mainly uses FPGA as the main controller, FPGA drives linear array CCD for liquid level sensor, CCD receives the light signal ,which is transmitted through the parallel light beam. Under the action of the driving sequence, the optical signal is converted into one dimension image signal which is easy to be processed by the self scanning mode. Then, the image signal is sent to the PC machine for processing. Last, by analyzing the relationship between the actual level and the image edge pixels, so the measurement of liquid level is realized. The experimental prove that the absolute accuracy of the system can reach 10μm, and the measurement resolution is better than 2 μm.