Rare-earth orthoferrites (such as YFeO3) with orthorhombic perovskite-type structure are promising candidates in the fields of electrode materials, gas sensors and photocatalysts. The geometric structure, the electronic structure and the optical properties of YFeO3 crystal are investigated by using the plane-wave pseudo-potential method, with the scheme of generalized gradient approximation, revised Perdew-Burke-Emzerhof exchange-correlation potential and ultrasoft pseudopotential. The obtained lattice parameters are in good accordance with experimental results reported. The results confirm that YFeO3 crystal is a direct semiconductor with a gap (Eg) of about 2.22 eV, based on the analyses about band structure, density of state, dielectric function, absorption coefficient, and photoconductivity. It is clarified that YFeO3 crystal and nanocrystalline possess good photocatalytic activities for visible light.