Abstract: RFM（refueling machine） is the main component which used to perform core loading/offloading in nuclear power plants. The kinematic verticality of RFM inner mast will directly affect the safety of fuel operation. By analyzing of RFM commissioning in a nuclear power plant, it is proved that the kinematic verticality of RFM inner mast can be accurately measured by a laser device. By the means of improving the mast installation verticality and the inner-outer mast concentricity, and accurately adjusting the inner-outer mast guide roller gap, the RFM inner mast kinematic verticality can be sufficiently improved, which will reduce the occurrence of fuel operation accidents.