Abstract: On the basis of the present methods of compaction testing, the mechanical model of a vibrating roller-soil system was analyzed and its dynamic equation was established. The relationship between vibration acceleration and soil rigidity and soil damp was obtained by simulation. Based on the simulation result, the auto-testing principle of compaction degree was put forward,i. e. through testing the vibration acceleration of the vibrating roller, the soil compaction status can be reflected indirectly. A auto-testing system was developed and applied to a project, and the strong relativity between soil compaction degree and vibration acceleration was verified.