A piecewise adaptive event-triggered mechanism was proposed for trajectory tracking of a class of nonholonomic wheeled mobile robots. Based on the kinematics model of the pose error of the nonholonomic wheeled mobile robot, a kinematic controller was designed, and Lyapunov stability theorem was used to prove the uniform stability of the control system. A piecewise event-triggered mechanism was proposed based on the controller, and constant and adaptive trigger threshold parameters were designed respectively in two time periods. Lyapunov function analysis method and Gronwall-Bellman inequality were used to prove that the closed-loop control system was uniformly ultimately bounded, and the two adjacent trigger intervals had positive lower bound. Finally, MATLAB simulation shows that the proposed method can adaptively adjust the trigger threshold parameters according to the system state error norm, and track the desired trajectory with a lower trigger frequency.