The invention discloses a spherical mechanism for a quad-rotor amphibious robot. The spherical mechanism is composed of a rotor wing mechanism and a spherical shell mechanism, wherein the rotor wing mechanism is composed of a long shaft, a short shaft, a base, four rotor wings and four motors, the spherical shell mechanism is composed of a flexible rod, two fixed bases and a rolling ring, the long shaft is perpendicular to the short shaft, the axis of the long shaft and the axis of the short shaft are located on the same plane, the four rotor wings and the motors are symmetrically installed on the long shaft and the short shaft, and a connecting shaft on the long shaft is connected with the fixed bases of the spherical shell mechanism to enable the rotor wing mechanism to rotate around the long shaft relative to the spherical shell mechanism. The rotor wing mechanism provides power for the robot, and the robot is made to fly in the air or roll on the ground by setting the rotating speed and direction of the four rotor wings. When the robot flies in the air, the spherical shell mechanism serves as a protecting device. When the robot rolls on the ground, the spherical shell mechanism serves as a protecting device and a rolling device. The spherical mechanism has the advantages of being simple in structure, practical, convenient to dismantle, convenient to maintain, low in cost and the like.