The invention relates to a guide disc locking device of a tube rolling mill, which solves the stability problem of the tube rolling mill during the rolling process, and comprises a guide disc bracket 1 which is installed on a stander 12, wherein a guide disc 13 is installed inside the guide disc bracket 1, and is characterized in that four guide disc locking mechanisms 2 consisting of a base 3, apin shaft 4, a hydraulic cylinder 5, a shaft 6, a compression block 7, a pin 8 and a supporting saddle 9 are symmetrically arranged at two sides of the guide disc 13 inside the guide disc bracket 1, and two rectangular holes U which are supplied for the compression blocks 7 to extend out of the guide disc bracket 1 are symmetrically arranged on two side planes of the guide disc bracket 1. Compared with the prior art, since the guide disc locking device is added, the guide disc can be more stable and firm during the working process; therefore, the craftwork performance of the tube rolling millcan be improved, and the quality of the steel tube is improved.