Taking advantage of the centrifugal microfluidic chip for biochemical analysis, an optical detection system based on absorbance detection technology is designed. The effect of the poor light output stability of xenon flash lamp on test results is reduced by dual wavelength detection. The chip is located precisely by synchronous trigger positioning in the detection process. The effect of sampling error on the test results is also analyzed. The test results show that the absorbance repeatability of the system is 0.0994% by dual wavelength detection; the locating error is extremely small, it is 0.1429% by synchronous trigger positioning; and the sampling error is lower than 2%, which meets the requirements of national standards. The system has the advantages of simple structure, easy integration, and stable and reliable test results, it is promising in medical diagnosis.microfluidic chip