The photocatalytic performance of Ba2ZnSe3 is investigated by means of density functional theory. The investigation confirms that Ba2ZnSe3 possesses large birefringence, considerable anisotropy in the optical response, and the absorption edge occurs in the visible region. The estimated optical band gap of Ba2ZnSe3 is about 2.70 eV, and the EPc and EPv are about -0.145 V(vs.NHE) and +2.605 V (vs.NHE), respectively. Thus, Ba2ZnSe3 possesses a high negative reduction potential of excited electrons due to its higher CB position, and hence, the location of the CBM and VBM accommodates the redox capacity. Thus, the Ba2ZnSe3 photocatalyst is expected to exhibit superior activity in visible-light-driven photocatalytic H-2 evolution. The electronic band structure shows high k-dispersion bands around the Fermi level, which implies low effective masses and, hence, the high mobility carriers enhance the charge transfer process. It was found that Ba2ZnSe3 possesses a great effective mass difference between electron (e(-)) and hole (h(+)), which can facilitate the e(-) and h(+) migration and separation, and finally improve the photocatalytic performance. The observed large mobility difference in Ba2ZnSe3 is useful to the separation of e(-) and h(+), reduction of the e(-) and h(+) recombination rate, and improvement of the photocatalytic activity. Thus, Ba2ZnSe3 could be a good photocatalyst due to rapid generation of e(-)-h(+) pairs with photoexcitation, and a high negative reduction potential of excited electrons due to its higher CB position. The excellent photocatalytic performance of Ba2ZnSe3 is due to hyperpolarizablity formed by ZnO4 tetrahedra and co-parallel BaSe7 polyhedra groups, and the layer structure favors the enhancement of the photocatalytic performance. The presence of the distorted (ZnO4)(4-) tetrahedral causes to increase the efficiency of the photocatalytic performance almost to double in comparison to other chalcogenide crystals. Based on these results, one can conclude that Ba2ZnSe3 satisfies all requirements to be an efficient photocatalyst. This will greatly improve the search efficiency and greatly help experiments to save resources in the exploration of new photocatalysts with good photocatalytic performance.