Firstly,IPsec is introduced and its shortage is analyzed.Secondly,as a new Protocol,the limited transmission protocol is put forward.In the new protocol,if many data packets are transmitted into the network by a computer,the computer would be limited to transmit data packets in order to assure the security of the network.Then,the performance of the new protocol is simulated with OPNET software,which shows the new protocol could enhance the network performance.For example,the average of HTTP object response time is 0.013s when the new protocol is adopted in the network.When the new protocol is not adopted,it is 0.032s.