Traveling wave velocity is the key to the measuring accuracy of the time-domain reflectometry cable length measurement system.To reduce the impact of velocity,the velocity characteristics of time domain reflectometry cable length measurement system are studied,the frequency characteristics of traveling wave propagation velocity and dielectric constant are analyzed,and the influence of cable material parameters and ambient temperature on traveling wave propagation velocity on cable is investigated.The basis for determining the wave velocity is summed up.The signal propagation velocity at different temperature is measured,and the temperature compensation coefficient of traveling wave propagation velocity in the PVC insulated cable is presented.Experimental results show that the measuring accuracy of the time-domain reflectometry cable length measurement system is improved significantly by velocity temperature compensation.