A method for measuring a data transmission speed, applied to a server side, is provided. The method includes: updating RTTs within a current sliding period upon receiving an ACK message from a client device; calculating a maximum RTT, a minimum RTT and an average RTT within the current sliding period; obtaining an amount of data in the latest RTT; calculating a minimum speed, a maximum speed and an average speed respectively, according to the amount of data in the latest RTT, and the maximum RTT, the minimum RTT and the average RTT within the current sliding period; calculating speed change gradient information according to the minimum speed, the maximum speed and the average speed; and calculating a speed prediction value according to the speed change gradient information. An apparatus for measuring a data transmission speed, a server-side device and a computer readable medium are provided.