The steric opacity function, which includes alignment and orientation effects, for the indirect ionization process of CH3Cl+ has been obtained and analyzed from the study of fast electron impact of the oriented CH3Cl molecule with the well-defined orientation of the JKM]) = 111] state. On the basis of a particle collision approximation for the projectile electron and the target molecular orbital electrons, both orientation and alignment dependences have been clarified by the ab initio calculations of the HOMO electron densities of the molecule. A good correlation between the site-specific ionization cross section and the cross section of the spatial distribution of 2e HOMO electrons of CH3Cl was confirmed.