Powder rotational molding technology has little evolved until recent years because it stood alone on the market of large hollow parts, in small series. Recently, the disengagement of specific materials suppliers in rotational molding and increase of competition from blow molding and thermoforming, has motivated industrials to develop a new process of non-reactive liquid rotational molding, aiming at the use of standard injection-molding polymer grades and at reducing cycle times. In this new process, the polymer is melted beforehand in a classical injection unit and injected into the rotating mold. This method is closer to liquid coating than to the liquid/powder rotational molding process. The main part of this new process is to predict the repartition of the melted liquid layer adhering to the mold wall. Numerical approach is considered. First, modelling the thin viscous film flow with Matlab shows the hydrodynamics stability criterion of the film flow, the mean flow velocity and allows to control the viscosity parameter and the speed ratio rotation for a functional process. Then, using numerical scheme of Lax-Friedrichs, the repartition of the thin film flow with gravity is modelled. The hydrodynamic stability is respected. The lubrication approximation is considered, surface tension and the component of gravity normal to the film plane are neglected. Results are then compared with the three dimensional numerical simulation by Finite-Volume StarCCM+ code. Results show that the process time is strongly dependent on the choice of primary and secondary rotation frequencies. Keywords: Rotational molding, injection, thin film, lubrication approximation.