The statistical distribution of natural phenomena is of great significance in studying the laws of nature. Here, in this paper, based on laser scattering particle counter, a simple random pulse signal generating and testing system is designed for studying the counting distributions of three typical objects including particles suspended in the air, standard particles, and background noises. Moreover, in order to have a deep understanding of the experimental results from laser scattering particle counter, a random process model is also proposed theoretically to study the random law of measured results. Both normal and lognormal distribution fittings are applied to analyze the experimental results, and we have proved that statistical amplitude and width distributions of particles suspended in the air, standard particles, and background noise match well with lognormal distribution when natural numbers are used as the variables. This study is an important reference for statistical data processing for laser scattering particle counter, moreover, it will also be a useful guide for designing laser scattering particle counter with high accuracy and processing speed.