Growth in the mobile services industry has remarkably increased in the number of mobile services provided, and present methods of service provision have proven insufficient to guide users efficiently to the services they need. To solve this problem, a Taskoriented menu, which enables users to search for services by ”what they want to do” instead of by “name of category”, has been proposed. Construction of such a Task-oriented menu is based on a task ontology modeling method which supports the description of user activity such as task execution and the solving of obstacles encountered during the task. This paper discusses a task ontology-based modeling method which supports the description of users’ activity and related knowledge such as how to solve problems that occurs on the users and prevention method for accidents. Models described by our method contribute to checking, designing and improving mobile internet services