In the diffusion absorption machines, there is not a mechanical pump for circulating the working fluid. This role is provided by the thermal bubble pump. The efficiency of diffusion absorption cycles is related of the pumping action of the bubble pump. The aim of the present numerical study is to investigate the influence of tube diameter, heat input, tube length and mass flow rate on the pumping action of solar bubble pump. A one-dimensional two-fluid model was developed under constant heat flux for predict the behaviour of pumping ratio under permanent regime. At a fixed bubble pump tube length of 1m, and ammonia mass fraction of 0.4 and pressure18 bar at the inlet, numerical results show that, the pumping ration is mostly influences by heat input. Its maximum is directly related by the mass flow rate and tube diameter.