Project-X, a proposed high intensity proton facility to support a world-leading program in neutrino and flavor physics at Fermilab, plans to use the existing FNAL recycler and main injector (MI) complex, but requires upgrading the MI RF syste m. Currently there are two proposed 53MHz RF cavity designs for 6GeV to 120GeV operation. One design is a straight-line quarter wave resonant cavity, and the other a tapered quarter wave resonant cavity. The electromagnetic (EM) simulations of the two cav ity designs are carried out by using SLAC finite element parallel code suit ACE3P. The EM simulation results for the RF parameters and higher-order-mode (HOM) properties have shown that the tapered cavity design has better RF performance than the straight one. The tapered cavity shape will then be optimized for the final design to meet the specified performance requirements for the Project-X. Possible multipacting zones in the cavity will be identified and the use of HOM dampers investigated for the optimized design. Show Partial Abstract