There are many white blood cell (WBC) classification methods in the research and development field of five classification blood analyzer and their functions are relatively perfect, but the majority of instrument structure is complex, and has more interference factors, and thus their stability and precision can not be guaranteed as a result. Therefore, an optical signal detection and processing system that is applied to the WBC five classification and uses the full-optical detection technology is proposed, taking the front side light scattering (FSC) and axial light absorption (ALL) as characteristics of cells, the photoelectric conversion circuit, filter and amplification circuit and analog/digital (A/D) conversion circuit are designed, and the five classification of WBC is completed. The blood analyzer using this system has the advantages of simple structure and high reliability. The test results show that the correlation r of the system for WBC classification is good, and the precision of the instrument is closed to Mythic 22, which is a high-grade five classification blood cell analyzer, and the function and performance of the instrument is perfect.