A Hojman conserved quantity constructed by using the special Lie symmetry, or the Noether symmetry, or the form invariance for a holonomic system in the event space is studied. First, the differential equations of motion of the system are established. Second, the critera of three kinds of symmetries, such as the Lie symmetry, the Noether symmetry and the form invariance, and the relation among them are obtained. Third, the conservation law theorem gained by Hojman is generalized and applied to the system, and a non-Noether conserved quantity is obtained. Two examples are finally given to illustrate the application of the results.