The invention discloses a method for bandwidth dynamic allocation. The method comprises the steps that a bandwidth allocation updating request is sent by a current service subsystem to a management subsystem; the management subsystem sends bandwidth change interrogating information to other service subsystems except the current service subsystem according to the bandwidth allocation updating request and obtains bandwidth usage efficiency of all the service subsystems from a load balancer; various service subsystems receiving the bandwidth change interrogating information returns bandwidth change comment information to the management subsystem; the management subsystem generates a bandwidth allocation strategy according to the received bandwidth change comment information and bandwidth usage efficiency of all the service subsystems; the management subsystem sends the generated bandwidth allocation strategy to the load balancer; the load balancer allocates the bandwidth for all the service subsystems according to the bandwidth allocation strategy. According to the method for the bandwidth dynamic allocation, the bandwidth of each service subsystem can be allocated dynamically according to service requirements of the service subsystems.