Two kinds of Al-Zn-Mg-Cu alloys containing Sc and Cr, Mn, Ti as well as Zr were prepared. The precipitation free zone (PFZ) around the second phase particle and the precipitation free band at grain boundary as well as the interaction between them were studied by transmitting electron microscopy (TEM). The equation for pinning force of single second phase particle to grain boundary was presented. Results show that when driving force for grain boundary migration exceeds the encumbrance force of particles and their circumference PFZs against the boundaries, grain boundaries are penetrated by particles to form holes. During grain boundaries sweep particles, their movement, e.g. acceleration stage and deceleration stage, undergoes two different stages. When the hole diameter is equal to the particle size, the encumbrance force is the least and the velocity of boundary migration is the highest. When the sum of grain boundary energy and surface phase boundary energy is equal to driving force, grain boundary is pinned by the particle and stops moving. Solute atoms diffusion takes on the trend from high-concentration zone to low-concentration zone; PFZ around grain boundaries and particles have great effect on migration of grain boundary.