Noether`s inverse theorem of Birkhoffian system was studied. The general solution that Noether`s symmetries can be deduced from the known conserved quantities for Birkhoffian system was proposed. The difficulties in the general solution were pointed. The special solutions for the inverse theorem were presented by introducing auxiliary equations, in which the conserved quantity and the symmetry are interrelated directly. An example was given to illustrate the application of the results.