Being the fastest and most convenient transportation between Hong Kong International Airport and the city, the Airport Express serves thousands of passengers every day. The “Real-time Train Seat Availability System” in Airport Express is launched in order to provide a pleasant and seamless journey for MTR passengers. It shows the real-time seat availability information of next arriving train via Passenger Information Display System located at the platforms of the Airport Express. Data Analytics, Machine Learning and Artificial Intelligence (AI) Technology was used to count passengers in each carriage during train departure. This paper outlines the system designs and architectures. Through this project, we would like to explore the potential possibilities in future deployment to different parts of the MTR network to enhance the travel experience of our customers.