The traditional optical particle counting method is limited by the bandwidth of particle echo pulse. Therefore, it cannot be directly applied to the measurement of particle number at the back end of the ultrafine particle condensation growth system. In this paper, based on the principle of particle light scattering, a particle optical counting module by using the scheme of high-bandwidth particle echo pulse is designed. At a sampling flow rate of 0.3 L·min ^-1, the echo pulse half-width of the 15 μm standard polystyrene particle is 650 ns, which improves the efficiency of particle counting. In order to improve the upper limit and accuracy of the particle number concentration measurement, a particle coincidence correction method based on probability statistics is proposed. The upper limit of the particle number concentration measurement is 2×10 ⁵ cm ^-3 by using this correction method. Experiments in the self-developed butanol-based ultrafine particle condensation growth system are conducted. The results show that the correlations between the self-developed system and the ambient air concentration measurement devices TSI-3788 and Airmous-A20 both exceed 0.98 , and in contrast, that between the self-developed system and the vehicle emission solid particle number concentration measurement device MEXA-200SPCS is up to 0.96. Thus, the accuracies of the designed optical particle counting module and the coincidence correction method are verified.