Since in some proposed quantitative models the detail feature of the mini circulation of design revision in product development process has not been described sufficiently, a new type of quantitative model based on the network of product process design activity pairs is proposed in this paper to describe the product development process in concurrent engineering. And the method of computing the mean duration of the product process design activity pair and the resource occupation rate of product or process design activity is proposed． Based on that，the problem of the planning of the product development proc ess in concurrent engineering is modeled as a resource—constrained project scheduling problem．Different from other resousce—constrained project scheduling problems，in this paper，the number of the resources allocated for the product development project is not pre—determined．but is ohtained along with the optimal product development plan．Therefore，this is an integrated optimization problem of the resource allocation and the planning of the product development process．A new algorithm based on branch—and—hound approach is proposed in this papef for solving the problem and a heuristic rule is introduced to improve the searching efficiency of the algorithm ．