1. A method, implemented on at least one computing device each of which has at least one processor, storage, and a communication platform connected to a network for evaluating query suggestion quality, the method comprising the steps of: providing a plurality of query suggestions in a ranking to a user; detecting a user activity with respect to one of the plurality of query suggestions; determining a position of the one of the plurality of query suggestions in the ranking; and calculating a quality measure of the plurality of query suggestions based, at least in part, on the user activity and the position of the one of the plurality of query suggestions.