Summary: Lacking effective web services or a chain of web services in web, a semantic web service discovery algorithm based on swarm system is proposed. Firstly, we assume that there is no central registry for services information and we use a distributed registry for storing services information. Then, in the case no single service can satisfy user request we will chain existing services to create a composite service answering user request. At last, we use VAR-GARCH (Vector Auto Regression Generalized Autoregressive Conditional Heteroskedasticity) model for service composition which incrementally gathers required services information and check them to satisfy a desired chain.