So,What's the difference between SOA and web services?

SOA is not Web services

There seems to be general confusion about the relationship between SOA and Web services. In an April 2003 Gartner report, Yefim V. Natis makes the distinction as follows: "Web services are about technology specifications, whereas SOA is a software design principle. Notably, Web services' WSDL is an SOA-suitable interface definition standard: this is where Web services and SOA fundamentally connect." Fundamentally, SOA is an architectural pattern, while Web services are services implemented using a set of standards; Web services is one of the ways you can implement SOA. The benefit of implementing SOA with Web services is that you achieve a platform-neutral approach to accessing services and better interoperability as more and more vendors support more and more Web services specifications.

In other words

SOA is the overarching strategy for building software applications inside a company—think of an architectural blueprint—except that in this case, the architecture calls for all the pieces of software to be built using a particular software development methodology, known as service-oriented programming. Web services, meanwhile, are a set of standard communication mechanisms built upon the World Wide Web. Web services are a linking and communications methodology. SOA is an overall IT strategy.