The invention discloses a network performance detection system. According to the invention, a measurement period is divided into a plurality of time slices; a plurality of shadow memories are correspondingly arranged for one state memory; therefore, in a measurement period, message dyeing operation is started for a plurality of service flows, the message dyeing operation of one service flow in each group of service flows is controlled to be started in each time slice, a system timestamp is stamped on a dyed message, and the system timestamp is sent to a server. Correspondingly, the invention further discloses a network performance testing method. According to the invention, the resources of the state memory can be flexibly expanded so as to meet the network performance test of more serviceflows.