A Product-Service System (PSS) is defined as a combined system to coincide with customer experience. However, due to the absence of a specified PSS design method, service design methods, such as service blueprint, are commonly applied for developing PSS design. In addition, they do not deal with the detailed activities of the interaction with products or the expectation around the use of PSS. In this research, a method to develop a new PSS concept is proposed through analysis of the correlation between the expectation and experience of an activity. This method is based on the system combining the basic unit of activity, expectation, and experience, and the two axis concept is used: one is related to the flow of activities and time, and the other is about the gap between the expectation and experience of an activity. Therefore, the purpose of this method is to satisfy the customer's expectation and needs by combining products and services based on an activity. A self-checkout system was chosen as an object of empirical research for the expectation and experience of a PSS activity. The activity is unitized into basic activities of using the self-checkout system. The structure of the expectation and experience, characteristics, and sequence of the activity are investigated. Hence, this research expects that the new method can be used as a development tool for designing an improved self-checkout system.