The design method of aerodynamic particle sizer which takes the ATMEGA128 chip as the control core is presented. ATMEGA128 chip is a kind of monolithic integrated circuit series of AVR single chip. The design method of hardware and software of this systerm is also given. The single chip communicates with computer to control the apparatus, analyze the aerosol particle and drive the LCD module to display the two-dimensional graph and status of the apparatus. Man-machine interaction is realized. At present, this system is in trial operation and prepared to invest in environmental gas monitoring.