Disclosed is an anchorage cable stretching automatic monitoring system and monitoring method. The stretching cable thrills through the ground jack center, a pull rod displacement sensor is installed outside the cylinder, a pressure sensor is installed on the oil return pipe, so as to convert measured displacement oil pressure into electrical signals, which are transmitted to the hardware platform for a long distance transmission, and a data acquisition module, a monitoring instrument host containing a central processing unit, a data memory and serial communicating ports, a motor drive module and a data automatic store and output system are set up in order. With programming control, a motor is used to control the opening of the oil valve to realize automatic stretching, and then the stretching velocity and oil pressure signal are used to control the rotary direction and velocity of the motor, thereby achieving controlling the oil pressure. The anchorage cable stretching automatic real time monitoring, feed back, automatic record and report forms print are realized, which not only greatly reduces work intensity and improves efficiency, but also effectively guarantees anchorage cable construction quality. An advanced high precision sensor is used to instead of the existing micrometer and pressure gauge, to realize the improvement of measurement approach, which is used in geotechnical engineering requiring prestressing force exerting and anchorage cable stretching.