By means of metallographic microscope and SEM the correlation between the feature of etch-pits and the grain orientations in bcc metals has been investigated. The grain orientations were determined by ECP in SEM and illustrated in a unit stereograph triangle. A series of their relational expressions was deduced with aid of vector analysis and coordinate transformation method. Some tables and charts, on which the grain orientation can be rapidly consulted, have been constructed by collection of the theoretically computed data. The analyzed results of the grain orientations may be directly expressed in a unit stereograph triangle and also easily determined on the transformation matrix of the grain boundaries, because the shapes of etch-pits are described by a continuous function of azimuth angle (θ, φ). Certain metallurgical problems have been discussed by the application of this analytical technique.