The paper deals with the mathematical modeling of the dynamics of a gas-particle mix in jet milling devices. The calculation methods developed allow performance analysis and design of the jet mills operating at different particle concentrations. Within the framework of the presented research the following areas have been studied numerically: (1) the stream in a nozzle; (2) the flow in a jet; (3) the jet-flat target interaction zone; (4) the vortex stream in a vortex chamber operating as a mill. A new model of particle friction against accelerating nozzle walls has also been proposed.