In this work, solar cells were simulated single, mechanically and monolithically stacked based on the CZTS (Se) 4 absorption layer, both layers of tandem solar cell were simulated using by AFORS-HET software (one-dimensional ). Electrical properties of the monolithical tandem cell, it's determined after the current matching to the top and bottom sub-cell. The short circuit current density Jsc is about 23.9 mA. cm-2 when the top cell thickness is 384 nm in conjunction with the 1000 nm bottom cell thickness. The maximum efficiency obtained is approximately 23.1% with an open circuit voltage Voc ~ 1146.9 mv. The efficiency of the mechanical tandem cell with series connection was 23.76 % at open circuit voltage Voc ~ 1166.9 mv and the efficiency about 26.62 % at open circuit voltage Voc ~ 475.2 mv for mechanical tandem cell with parallel connection when the both cells had the same thickness(1000nm)..