A model of passive impurity plume is considered in the homogeneous turbulent atmosphere with accounting for in-plume fluctuations of the impurity concentration. The model is based on the method of random forces of the turbulence theory and allows calculating the space–time correlation functions of the concentration field. It is shown that the in-plume concentration fluctuations are caused by longitudinal pulsations of the wind velocity. The plume axis fluctuations are caused by transversal pulsations of the wind velocity with the scales equal to typical displacement of a liquid particle due to the turbulent diffusion in the average wind direction. The amplitude of the plume axis fluctuations tends to zero at large distances from the impurity source. At small distances from the source, where the main contribution to the impurity concentration pulsations is made by the plume displacements as a whole, the considered model is close to the Gifford plume model. At large distances, where the in-plume concentration fluctuations are considerable, the indicated models differ much. In particular, the time correlation function of concentration pulsations can be negative in distant plume regions. The calculation results satisfactorily agree with the experiment.