In this paper, the differential variational principles of mechanical systems in the event space are studied. The D'Alembert-Lagrange principle, the Jourdain principle, the Gauss principle and the universal D'Alembert principle in the event space are established on the basis of the D'Alembert principle of the system. The parametric forms of Euler-Lagrange, Nielsen and Appell for these principles are given, and the parametric form of Mangeron-Deleanu for the universal D'Alembert principle is deduced.