Abstract: The Mei symmetry and conserved quantity of the second-order Lagrange system on time scales have been studied. Based on the motion equation of the second-order Lagrange system on time scales, the Mei symmetry of the second-order Lagrange system under infinitely small transformation has been explored. The definition of Mei symmetry and the decision equation of the second-order Lagrange system on time scales are obtained. And the conditions for the conserved quantity caused by Mei symmetry is established. An example is given to illustrate the application of the theorem.