In this paper, the symmetries and a new type of conserved quantities called Mei conserved quantities for systems of generalized classical mechanics are studied. In the high-dimensional extended phase space, the differential equations of motion of the systems are established, and the criteria for Mei symmetries, Noethe r symmetries and Lie symmetries of the systems are given. The conditions, under which the above three symmetries can respectively lead to the Mei conserved qu antities, and the form of the Mei conserved quantities are obtained. Finally, an example is given to illustrate the application of the results.