Solar thermal propulsion (STP) is a form of spacecraft propulsion that makes use of solar power to directly heat propellant, and does not require an electrical generator as most other forms of solar-powered propulsion do.Therefore, its structure is relatively simple and it has a high solar energy utilizing efficiency.Solar thermal propulsion has performance advantages of high specific impulse and moderate thrust levels.Consequently, solar thermal propulsion has the tremendously developmental potential to be the propulsion of to-be micro-satellites/nano-satellites and improve kinds of special mission levels.Solar thermal propulsion is mainly composed of solar concentrator, absorber/thruster and propellant supply system. Solar thermal propulsion is the utilization of concentrated Sunlight for the purposes of heating a propellant to high temperatures via a heat exchanger. The heated propellant is fed through a conventional rocket nozzle to produce thrust. Sunlight concentration is achieved via an optical concentrating system, such as a series of lenses or mirrors. This concentrated sunlight impinges on a blackbody cavity receiver, which is subsequently heated to high temperatures.A propellant feed system causes a monopropellant to flow around the cavity receiver where heat is exchanged from the receiver to the propellant.This paper simulated propellant flow of absorber/thruster of solar thermal propulsion system, such as flow distribution of hydrogen and flow distribution of ammonia. According to comparing simulant results with theoretical results, it is found that the results of simulation are in good agreement with ones of theory, which explains the rationality of nozzle structure, equal wall-temperature model and numeration method.At the same time, the factors influencing performance of STP system were analyzed, such as throat diameter, convergent half angle, divergent half angle and wall temperature.It has important meaning for the design and further research of STP.