Methods, systems, and programming for targeted advertising and conversion measurement. In one example, first information related to an online activity of a user is received. The online activity is associated with a first attribute to be used to identify the user. Second information related to an offline activity of the user is received. The offline activity is associated with a second attribute to be used to identify the user. A connection between the online activity and the offline activity of the user is then identified by matching the first attribute with the second attribute. A profile of the user is obtained based, at least in part, on the identified connection. A request of serving an advertisement is received. The user is selected from a plurality of users based on the profile of the user and information related to the request. The advertisement is provided to the user.