Taking video conference service as an example, a resource reservation algorithm that could reduce bandwidth was proposed, in order to solve the problem of service quality assurance for large-capacity and low-latency video services in the core network in the future. The video conference requests were resolved into multiple resource requests, and then the bandwidth resource was reserved in advance in units of time slots, under the core network architecture based on software defined network. When making bandwidth reservation, if it was found that the link did not meet the bandwidth requirements of the video service within a certain time scale, the bandwidth reduction method would be adopted to avoid the reservation failure problem caused by the insufficient bandwidth demand in a short period of time. The simulation experimental results show that, compared with the dynamic resource algorithm without bandwidth reduction, this algorithm can effectively improve the success rate of video service resource reservations; the greater the number of participants and the smaller the time slot, the greater the improvement of the success rate will be.