Smoking is harmful to health. But quitting smoking is difficult. The aim of this project is to make an application that helps people giving up smoking. Different from other quitting-smoke applications, DuoQuitter does not help smoker by showing their health status when use it. For people who want to quit smoke, the thing they cared most is the number of the days they are not smoking. Therefore, remind users how many days they keep away from smoking is the key function in DuoQuitter. Using this application, users can also add another quitter as their partner. Partners can encourage and compete with each other. The number of days they quitting is the main comparative data since they becoming partners. With encourage and competition, quit smoking will succeed.