Abstarct: Nuclear battery is a device that convert the energy that is released from radioactive decay to electric energy[1]. This kind of battery divides into the three groups; direct convert, indirect convert, and direct charge nuclear battery. High energy density and high longevity are the advantages of nuclear batteries [2,3]. The first nuclear battery was a direct charge nuclear battery that was built by moseley in 1913 . In this research we study about the factors that affect on increasing the efficiency of direct charge nuclear battery with simulating parts of it with MCNP4C code. In this kind of battery the charged particles that emit from a radioactive source collect directly with a plane in front of source. The activities that have done for increasing the efficiency of this kind of battery was, selecting the proper material for radioactive source in this kind of battery, selecting the proper geometric shape for battery, selecting proper materials for substrate and side cover to increasing the efficiency of source, selecting the proper material for use in surface cover of collector to increase its efficiency and also estimation of effective thickness of substrate and side cover of source and surface cover of collector. Finally we achieve to efficiency of 16.5%, this amount have 37% relative increasing in compare of latest works that have almost efficiency of 12%.