Using Yeh's matrix formalism, the approximate formulas for the magneto-optical effects in reflection from semi-infinite orthorhombic crystal with symmetry axes parallel to the Cartesian axes are derived for a general orientation of the magnetization vector. The magneto-optical (MO) effects in such structures are usually calculated numerically, but theoretical formulas give us physical insight into these effects and an good understanding of their symmetry properties. The near normal incidence approximation allows to study effects, which appear in the case of small angle of incidence in the contrast to the normal incidence. Different dependencies of these effects on the sample rotation allow us to distinguish between trigonal, tertragonal and hexagonal structures including and missing two-fold in-plane symmetry axis. The theoretical description of the magneto-optical effects can be applied to the magneto-optical ellipsometry, which is very sensitive nondestructive methods suitable for study of magnetic anisotropy, magnetization reversal properties of nanostructures, and exchange coupling.