Abstract: By theoretical analysis of potential and electric field distribution of a gyrotron electron beam, the formula of velocity ratio measurements is presented. The electron beam is equivalent to transmission-line inner conductor. A ceramic capacitance divider is proposed for velocity ratio measurements. The design and processing technique of the measurement system, the calibration method and result interpretation of the ceramic capacitance divider are presented. At last, the result of primary experiment is introduced. Capacitance divider was selected for the velocity ratio measurement because it does not perturb the electron beam and normal operation of the gyrotron is preserved as a result. This technology can be used to guide the design of magnetron injection gun and the gyrotron experiments.