The invention discloses a semi-automatic torsion straightening machine for a T-shaped guide rail. The semi-automatic torsion straightening machine comprises a main platform. The machine is characterized in that: a guide rail torsion device, a front torsion detection device, a front mechanical arm centring device, a rear torsion detection device, a rear mechanical arm centring device and a guide rail pushing device are sequentially arranged on the main platform along an axial direction; at least one lifting platform and at least one guide rail supporting platform are also arranged on the main platform; and torsion reference correcting devices are arranged on one side of the front torsion detection device and one side of the rear torsion detection device respectively. In the semi-automatic torsion straightening machine, the torsion of two ends of the T-shaped guide rail is measured by electronic contacts of dial indicators in the front and rear torsion detection devices, data is then transmitted to a personal computer (PC) control device for computation, and finally, a control signal is output to the guide rail torsion device according to a measurement result for performing torsion straightening on the T-shaped guide rail. Compared with the conventional manual measurement, the semi-automatic torsion straightening machine is high in measurement accuracy, simple in structure, convenient in operation and very high in degree of automation, and is quite practical.