The invention discloses a steam turbine radial flow clearance measurement method. The method comprises a step of placing silica gel in a measuring position and buckling a baffle plate, a step of lifting an upper baffle plate, removing the silica gel to measure the thickness of indentation, and obtaining a radial flow clearance initial value A0, a step of installing a contact sensor on the upper baffle plate, buckling the upper baffle plate again, allowing the contact sensor and a rotor to be in contact, recording the radial flow clearance value A1 displayed by the contact sensor at the moment, fastening a baffle plate split bolt, buckling an upper cylinder, fastening a cylinder split bolt and then recording the radial flow clearance value A2 displayed by the contact sensor at the moment, and calculating a baffle plate center change difference A3=A2-A1, and a step of calculating a radial flow clearance value A=A0+A3, and adjusting a baffle plate process hanging pin pad according to the radial flow clearance value A. According to the method, repeated measurement work is avoided, the method is precise and the construction period is saved, the cost of use and maintenance is relatively low, and the method is easy to popularize.