A racket stringing machine comprises includes a horizontal adjustment device and a brake device. The adjustment device is fixed to a base by a horizontal mounting seat which includes a horizontal rail and a base plate with one end slidably mounted to the rail. Thus, the string pulling device can be horizontally moved to adjust the angle of the string relative to the racket, so as to eliminate the friction between the string and the racket, improving the stringing quality and extending life of the racket frame. The brake device includes a disc and a clamping device disposed on a rotary shaft of the base. The clamping device is connected to hand and foot switches by two brake cables. When the operator leaves or stops the machine for a while during a stringing operation, he can stop the stringing operation conveniently by using the hand or foot switch.