Pure rolling single arc gear is a new type of circular arc gear. In order to study its vibration characteristics, the threedimensional solid model of pure rolling single arc gear was established using Pro/E. Then, the modal analysis of the gear was introduced into the ANSYS, and the natural frequency, vibration mode and critical speed of the pure rolling convex circular arc gear and concave circular arc gear were obtained. The natural frequency of gears with different teeth number, modulus and helix angle is the basis for the optimization design and dynamics research of the pure rolling single arc gear.