The nanoparticles terminated with pyramids firstly generate at the early stage of hydrothermal process; subsequently, a number of seed-crystals branch on the pyramids, furthermore, the homo-epitaxy based on which along the direction results in the formation of nanorods; finally, due to the extremely low concentration of Zn source, instead of the continual elongation of the nanorods, the nanotips dispersively occur on the top flat plane of nanorods as a result of selective epitaxy.