The dynamical change of cellular mechanical properties plays an important role in cell metastasis process, while how the cancer cells modulate their mechanical properties during metastasis are still not fully understood. In this report, the cellular detaching and seeding processes, two vital steps of cell metastasis, were simulated in vitro using a self-developed protocol and characterized by the dynamical mechanical properties using AFM. The measured results show that cells decrease their stiffness and increase their surface adhesion force as they are detaching from substrate, while cells present an opposite change in mechanical properties as they seeding. Additionally, the effect of anti-cancer drug (docetaxel) on the detaching and attaching process of cancer cells (PC-3) was also investigated from the aspect of mechanical properties. The results shows that the docetaxel can increase stiffness, decrease surface adhesion force of PC-3 cell, and slow down the change speed of these mechanical properties during PC-3 cell detaching and seeding process. These discoveries demonstrated that a dynamical change of cell mechanical properties is required for cancer cell metastasis, which provide a new drug development strategy for cancer treatment.