Abstarct: Nuclear converter is a device that transform energy from radioactive decay into electrical energy. High energy density and high longevity are the advantages of nuclear batteries. The attempts for prolonging the lifetime and power density of a nuclear converter began in the early 1900s after discovery of radiation, which has been continuing into the present. The first nuclear converter, which was part of a non- thermal converter (nuclear battery), was built by Moseley in 1913. The purpose of this research is to design of optimal geometric shape Direct Charge-Betavoltaic Liquid nuclear battery. First, the beta spectrum of source was calculated using the golden rule of Fermi and computer code in the Fortran language. Then, the effective factors on the efficiency of this battery were studied by simulation MCNPX code. In this battery, two 63Ni and 35S radioactive solutions with a concentration of 0.1 Molar were considered as source. Also, the geometric shape of the source was studied and optimized, in three states. The work done to increase the efficiency of this type of battery are: selection the proper material for radioactive source in this kind of battery, selection proper materials for substrate and side cover to increasing the efficiency of source, selection the proper geometric shape for battery, selection of proper material for use as an electrode, selection the proper semiconductor for use as a converter and determine the amount of doping. Finally, the betavoltaic nuclear battery was designed and optimized in two spherical and cylindrical models. The betavoltaic nuclear battery of the spherical model with the short circuit current of 0.926 nA and an efficiency of 2.513 % compared to the cylindrical model, with the short circuit current of 0.705 nA and an efficiency of 2.235 %, have the highest short circuit current and efficiency.