In order to improve economic benefits of platforms in competition, this paper discusses the problem on value-added service investment. The B2C platform competition model based on multi-homing is built. The result shows that, when platforms’ two sides are single-homing or the platforms' one side is multi-homing, the optimal investment meets on an interval strategy: If investment resources are less than the lower bound, the total resources or partial resources will be applied to value-added service according to one threshold of the marginal cost of investment. If investment resources are more than the upper bound, it will result in two pure strategy equilibriums. If investment resources are within the interval, a unique Nash equilibrium can be achieved. Moreover, when platforms’two sides are multi-homing, the optimal investment meets a single threshold strategy: If the marginal cost of investment is less than a threshold, the total resources of platform enterprise will be applied to value-added service, if not, partial resources will be applied.