In this paper, we study temperature effect on the laminar flow of an incompressible thermoviscous fluid in a conical diffuser. As a result of numerical simulation, velocity, temperature, and viscosity distributions in the diffuser channel were obtained, as well as the velocity profiles of the thermoviscous liquid flow for various sections. The influence of the channel geometry, temperature field and parameters of the dependence of viscosity on temperature on the hydrodynamic characteristics of the flow in a diffuser is studied.