The utility model discloses a servo control device of a rock mass true triaxial test at site, which comprises an axial pressure loading system, a confining pressure loading system and a measuring and collecting control system. Steel plates are horizontally placed on the top of a columnar rock mass sample at the site of an underground chamber, at least two or more than two jacks are evenly distributed on the steel plates, the steel plates are horizontally arranged on each jack, and the steel plates are provided with force transmission columns, the steel plates are horizontally placed on the force transmission columns, and the top of the force transmission columns abut against the rock mass surface of chamber. The length of the columnar rock mass sample ranges from 30cm to 100cm, the width ranges from 30cm to 100cm, and the height ranges from 60cm to 150cm. One end of a testing rod is arranged at the center of the top of the columnar rock mass sample, the other end of the testing rod penetrates through the steel plate holes and is connected with the measuring and collecting control system, and the jacks are connected with an axial pressure loading servo control system. By adopting a large dimension rock mass sample at the site of the underground chamber, high axial pressure is provided through the large tonnage jacks, and the servo control device is born by the rock mass at site. The rock mass true triaxial test is undergone under complex stress conditions, servo control can be loaded independently, and more accurate rock mass comprehensive strength is obtained.