A method, a server and a system for calculating bandwidth of UDP-based streaming media network transmission. The method includes: dividing video frame data to be sent into a plurality of sub-video frame packets, sending a sub-video frame packet with a preset serial number to a client, and receiving a response message sent by the client, wherein the response message includes a first serial number and a second serial number; sending a sub-video frame packet corresponding to the first serial number to the client, and determining whether the client has received all sub-video frame packets of the video frame data; if so, accurately calculating the actual bandwidth of the current network based on the sending start time of the first sub-video frame packet of the video frame data, the sending end time of the last sub-video frame packet of the video frame data and the size of the video frame data, which provides a basis for the self-adaption of the encoding rate.