Ex ternality is u sually to be in econom ical act ivit ies, and p roduct ive ex ternality can u sually be found in the conduct s of f irm s. A s one of the mo st impo rtan t o rgan izat ion fo rm s, indu st rial group shou ld be studied deep ly and system at ically, specially the fo rm at ive cau sat ion of indu st rial group. A cco rding to ou r researches, the vert ical ex ternality in the indu st rial relat ion sh ip s wou ld cau ses the fo rm ing of vert ical indu st rial group , and the ho rizon tal ex ternality wou ld cau ses the fo rm ing of ho rizon tal indu st rial groups.