A method for controlling data flow by a proxy server connected between a User Equipment (UE) and a content server is disclosed. The proxy server estimates a first amount of data reception indicating an amount of data received by the UE and calculates a second amount of data reception indicating an amount of data received by the proxy server from the content server. The proxy server delays transmission of acknowledgement (ACK) on data received by the proxy server from the content server and waits until a time allowed for the transmission, if the second amount of data reception is greater than the first amount of data reception by a predetermined threshold. The resent disclosure may prevent a waste of network load and unnecessary resources by the proxy server controlling download data rate from the content server.