Trimethylaluminum (TMAl) pre-seeding time, an important factor in controlling the quality such as morphology and dislocation of AlN on Si(111) substrate, was systematically investigated. It was revealed that different TMAl pre-seeding time indeed lead to substantially different AlN quality in terms of morphology and threading dislocations. For the optimized TMAl pre-seeding time 40 s in this work, the interface between AlN and Si(111) substrate without an amorphous layer was evidenced which is believed to be beneficial for growing high-quality AlN. A mechanism is proposed to explain the effect of the TMAl pre-seeding on AlN epitaxy on Si(111) substrate.