Semantic web service technologies have been proposed to enable automatic web service discovery and composition. But such approaches are suffered from significant effort to construct domain ontologies and to annotate web services with semantics by third parties. Hence social and collaborative tagging systems have been gaining the popularity on the web. Folksonomy-based web service annotating is emerging, i.e. to annotate web services with semantic from community-generated folksonomies. This paper focuses on how to provide folksonomy-based in-depth annotation of web services. Herein, the in-depth means the annotation is based on a structured folksonomy, and steps inside different parts of the web services in an automatic way. Two problems need addressed: exploring semantics for the folksonomy from original tags of web services, and automatically assigning tags to the different parts of web services. The paper proposes an approach to achieving automatic tags assignment of web services with a structured folksonomy. Such in-depth annotation facilitates web services discovery and composition by providing precise tagging of input, output and etc. A case-study and result of experiments on the pairs of tag-service extracted from a web service portal, seekda, illustrates the effectiveness of the approach.