Abstract: Aimed at the uneven flow distribution occurred in the solar tower receiver under variable load conditions, a calculation model suitable for the unsteady flow distribution of the parallel pipe system was established. On one hand, the variation of fluid parameters in the receiver with time under variable load conditions such as the weather change and the alternation of day with night was considered by introducing a time term into the discrete control equations. On the other hand, the effects of both the solar heat flux distribution and the manifold-pipes structure on flow distribution were simultaneously taken into account by the meshing of the whole flow domain including the manifolds and the branch pipes, as well as the coupling solution between the manifolds and branch pipes. The present model was then verified by the experimental data in the open literature. By using the present model, the effect of non-uniform heat load distribution on the steady flow distribution characteristics of solar receiver was studied. Then the dynamic variation characteristics of mass flow distribution in parallel pipes with step increase of boundary conditions such as inlet fluid pressure, inlet fluid temperature and solar heat flux were simulated. It was found that the flow distribution always tends to deteriorate sharply during the unsteady process, which brings great safety hazard to the operation of the solar receiver.