Abstract: For the sliding gap between the diaphragm and the groove center caused by the deformation of the high and medium pressure cylinders body in steam turbines after a long period operation, a multi-point data measuring device that can measure data of the cylinder and the diaphragm-groove center under the full load condition with combined high and medium pressure cylinders was designed, and the measuring effect of the device was verified by field test. Actual application results show that the device can make the main shaft precisely stay at the ideal angular position, and accurately measure the gap data by laser detector head. Compared with the reference value, the average deviation is within 0.01 mm. By applying this device, the measure time is decreased effectively, the accuracy and success rate of one successful adjustment at the first time are improved, and the safety and economy of unit are improved.