Research on intelligent tires has advanced as a system for monitoring tires and road surface conditions by installing sensors on tires. With respect to the monitoring of the road surface condition in particular, a technique for monitoring the road surface condition from the acceleration sensor installed in the tire has been developed. On the other hand, attempts have been made to sense the road surface condition from electrical changes caused by interaction between the tire and the road surface by using the tire itself as a sensor without setting a sensor device in the tire itself. In our research using Quasi-Electrostatic Field (QEF), phenomena have been confirmed, but no mechanisms and modelling have been established. In this research, we propose basic mechanism and model for road surface condition detection using QEF technology and verify them by vehicle test.