Copper-mold suction casting was employed to prepare the Cu56.4Zr31.02Ti6.58Al6 bulk metallic glass (BMGs). X-ray diffraction (XRD), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC) were used to analyze their microstructure, activation energy and crystallization mechanism. The criterions y(a) and z(a) were applied to test the validity of different nucleation-growth models for the first crystallization stage of the BMGs. Results show that the primary crystallization product of Cu56.4Zr31.02Ti6.58Al6 is Cu10Zr7 and the Starink-Zahra model can describe the crystallization mechanism well. Fitting parameters show that impingement effect factor λi≠0, indicating that impingement effect can't be ignored. Avrami exponent n decreases to 2.3 from 2.5, suggesting that the BMG experienced a continuous nucleation process and diffusion controlled growth process. Furthermore, the nucleation rate has a decrease trend.