Bid optimization, which aims to find the competitive bid to achieve the best performance for the advertiser, is an important problem in online advertising. The optimal bid recommendation enables the advertisers to make informed decisions without actually spending the budget. In this paper, we consider a bid optimization scenario that the advertiser’s budget can be split across multiple campaigns. To achieve the optimal performance, we formalize the bid optimization problem as a constraint combinational optimization problem, and derive an effective method to solve it. Experiment studies on realworld ad campaigns demonstrate the effectiveness of our method.