Abstract: Study on budget of expense for large complex systems is the primary problem in the filed of cost analysis.Weibull timedependent expense model is an econometric model about manpower and finance for large complex systems,and also called life cycle model.In this paper Weibull distribution characteristics,parameter estimation methods and several models are studied,Weibull theoretical explanation are given.Finally,a case is analyzed,by making use of experience estimation method to estimate characteristic parameter,then gain R&D expense budget distribution.It provides that the distribution can well accord with the practical system in project budget stage.