Abstract: Fracture analysis of coatings has an important role on the investigation of coating's failure mechanism,the optimization of the processing parameters and the design. The fracture of plasma sprayed wollastonite coatings was observed in-situ by using a scanning electron microscope (SEM) during the tapered double cantilever beam (TDCB) specimens were pulled open. Additionally,the effect of powder size on the coating's fracture toughness is investigated based on the observation of the microstructure,fracture morphology and cracking propagation of coatings. It was found that the cracking path was mainly influenced by the applied stress. The original pores in the coatings, including the large pores,cracks and non-bounded interfaces could guide the cracking somewhat. The fracture toughness of coatings increased and fracture paths were more curved with the decreasing of powder size.