In this paper, compared with the present calibration procedures performed by the metrology facilities and optical particle counter manufactures, the recommended calibration method of optical particle counters (OPC), which are operated on the principle of light scattering by individual particles and widely used in clean-room monitoring, air pollution control and laboratory aerosol studies is discussed. Based on referencing international standards and verified in more than several models of particle counters widely used in China, the calibration methods recommended here include inlet sample flow rate, repeatability, error of particle concentration and particle sizing accuracy.