The laser-monitoring observation method was used to measure the solubility of Octogen(HMX) in γ-butyrolactone. The relation of the solubility vs temperature were established according to Apelblat empirical equation by the linear least squares method. The effects of saturation temperature, stirring speed and cooling rate on metastable zone width were explored. The nucleation series effected by cooling rate and stirring speed were calculated based on the classical nucleation theory. The results show that in the crystallization process of HMX, the metastable zone width significantly broadens with the increase of saturation temperature and cooling rate and narrows with the increase of stirring speed. The nucleation series effected by colling rate and stirring speed are related to the saturation temperature. The nucleation series gradually become smaller with the increase of saturation temperature. Appropriate cooling crystallization conditions of HMX in γ-butyrolactone are the saturation temperature of 40 ℃, cooling rate of 0.1-0.2 ℃·min^-1 and stirring speed of 400 r·min^-1.