Abstract: The model of the synthetical benefit of a spacecraft is a dyna- mic model which is established by applying system idea and investment -expense theory.It includs the general benefit model and optimun benefit model.The value of synthetical benefit can be obtained by using system analysis and practising in satellite,platform and space station.And compared with engineering estimation methods the quantitative calculation of the dynamic benefit model is proved to be viable and creditble.It has certain general meaning for benefit analysis and calculation.It also indicates that in order to obtain the more benefit of space technology,not only a large amount of investment is needed,but also the investment stratagy must be considered carefully.In the whole investment period it is a good approach of raise benefit to maintain saturated level variable.It is also a important research topic which must be emphasized.