PM2.5 detection system based on light scattering method has the advantages, such as simple principle, simple data acquisition and processing and accurate measurement results, so it is one of the main methods of PM2.5 detection. Modularization design is adopted in PM2.5 detection system which is composed of four parts such as photoelectric acquisition, control and processing, display and warning and power modules. And PM2.5 monitoring and warning in real-time are realized. Proteus simulation results show that the system has accurate detection ability and the error is within the range of control. After hardware debugging and testing of the system, the PM2.5 particles number can be displayed in real time. When the particles number reaches a predetermined value, the buzzer warns.