Abstract: A search engine is developed.The use case，class，state and package diagrams of UML are used to do the requirement analysis and design of the system.The state diagrams are enriched by means of the OCL expressions.This system is programmed in C# and ASP.NET，with SQL Server for storing information，and is run in the Microsoft .NET environment.Following the object-oriented methodology，such as refinement and modularization，in building the UML/OCL models and constructing the program，the system is hierarchically divided into modules of particular functions.The system consists of a collector，an indexer and a searcher.They are respectively responsible for information gathering，information analysis and index constructing，and user interface.The paper reports on the ideas and process of the system analysis，design and implementation.