Numerical calculation and theoretical study on high optical absorption material BaSi2 based np or nip homojunction solar cells were conducted by using AMPS software. The effects of doping concentration and front layer thickness on the performance of n-BaSi2/p-BaSi2 homojunciton solar cell were comprehensive investigated. It was found that the donor concentration and thickness of n-BaSi2 had decisive influence on the light performance of n-BaSi2/p-BaSi2 homojunciton solar cell, since high donor concentration in n-BaSi2 gave rise to extremely high hole trapping concentration in n-BaSi2 and thus reduced the hole current as well as total current density under light illumination. Consequently, the n-BaSi2 layer was suggested to be designed either with low donor concentration or with thin thickness to achieve high power conversion efficiency. Same effect of n-BaSi2 on the performance of nip homojucntion solar cell was also observed. Contrarily, the optimized p-BaSi2 was suggested to possess high acceptor concentration and to be slightly thicker, in order to maintain the high built-in potential as well as Voc of nip homojunciton solar cell. On account of the front and rear contact barrier height between electrode and BaSi2 functional layer, the barrier height between p-BaSi2 and rear contact electrode had comparably more sensitive influence to attenuate the built-in potential and thus the Voc of BaSi2 based nip the solar cell. However, this negative influence caused by high barrier height could be convincingly conquered by employing thick p-BaSi2 layer.