Multi-beam satellite communication system can provide mobile users with global communication services.However,the on-board resource utilization is low due to the limited resources as well as the long distance between satellites and the earth,and the resulted time delay in service transmission.To address this,we propose a new downlink resource allocation algorithm for a multi-beam satellite communication system with beam interference,which is designed under two constraints of strict service delay and limited maximum interference power.Meanwhile,the influence of inter-beam interference on the system capacity is considered,and the Lagrange duality theory and sub-gradient descent method are used to obtain the optimal resource allocation strategy in order to maximize the service capacity of spot beam.The simulation results show that under the same noise power spectral density channel,the proposed algorithm meets the time delay requirement for each spot beam,has good fairness,improves the system in total transmission rate,and reduces the difference between the spot beam service demand and the allocated communication resources,therefore can provide maximized communication service to users;while under the condition of different noise power spectral densities,the proposed algorithm still maintains good fairness.