Microwave and radio-frequency thermal ablation has become an important means for tumor treatment. Real-time and precise monitoring of the change of temperature and thermal coagulation zones in thermal ablation of tumors is the key to ensure the safety of treatment and to achieve satisfactory curative effect. The ultrasound-based noninvasive monitoring techniques for thermal therapy are always a hot point of research. As a new ultrasonic tissue characterization method, ultrasound elasticity imaging is paid increasing attention in respect of the noninvasive monitoring of thermal therapy. In this paper, we introduce the principles and methods of noninvasive monitoring based on static elasticity imaging, acoustic radiation force elasticity imaging, and electrode motion elasticity imaging. We also summarize the state of the research home and abroad, and the prospect in these respects: how to achieve in vivo monitoring, how to incorporate the use of existing commercial ultrasonic diagnosis systems, how to combine temperature measurement with coagulation zone monitoring effectively, how to improve the capability of resistance to motion artifact ability, and how to increase the real-time performance and accuracy of monitoring.