Abstract: Fineness of pulverized coal is an important daily supervision and inspection item for pulverized coal as fired of thermal power plants. It is of great significance to supervise the normal operation of the pulverizer, guide the combustion of pulverized coal in the boiler, and ensure the safe, economical and environmentally friendly operation of the coal-fired unit. At present, the methods for measuring the fineness of pulverized coal in thermal power plants mainly include sieving method, laser diffraction method and online measurement method, etc. Among them, the laser diffraction method has the advantages of short measurement cycle, high accuracy and convenient operation. Most of the publicly reported studies on the laser diffraction method for determining fineness of pulverized coal use wet injection method, while pulverized coal in thermal power plants is actually used in a dry powder state, and pulverized coal may swell when immersed in a solution.In order to further study and establish a method for determining the fineness of pulverized coal using dry injection by laser diffraction method, the effects of parameters such as data collection time, dispersion pressure, and shading degree on the measurement results of pulverized coal fineness were studied, and the optimal measurement conditions were determined to be:collection time of 5 s, dispersion pressure of 0.3 MPa, and shading degree of 2% to 5%. At the same time, collaborative experiments were carried out to compare and analyze the measurement results of the laser diffraction method and the sieving method. The results showed that the dry injection laser diffraction method was accurate, simple and repeatable, and suitable for the determination pf fineness of pulverized coal.