Aiming at the problem of nano-scale particle concentration detection in the environment, the condensed particle counter was researched and designed. Firstly, the growth principle and detection principle of condensed particles were researched, and the growth device of condensed particle counter was designed according to the heteronuclear principle. Secondly, the signal processing circuit of the sensor was designed to solve the problem of poor anti-interference ability and difficult measurement of weak signal of particle detection. Then, a control system based on anti-saturation integral PID was designed to realize the closed-loop control of sampling flow. Finally, a prototype of condensed particle counter was developed, and several experiments were carried out, including flow control, nano-scale particle growth and counting. The experimental results show that the flow stability of the condensation particle counter designed is within 2%, and the relative error of counting with the TSI3772 condensation particle counter as the standard instrument is within ±8.5%, which meets the requirements of the industry standard.