Professional service firms has been regarded as prototypes of knowledge economy and "future enterprise" (Boussebaa& Faulconbridge, 2019) [1] . With the development of digital technology and rapidly changing external environment, companies face great challenges. Especially when the Covid-19 pandemic stoke the world. Previous researches indicated valid relation between corporate strategy and firm performance. (Porter, 1991 [2] ; Park, Shin and Jurn, 2009 [3] ). This article adopted quantitative analysis, taking three professional service firms as case studies. Secondary data is collected through financial reports, and official websites of the three companies. It is revealed that the largest professional service firms, though striving with the VUCA environment, managed to maintain a profit. Based on acquired information, the author first made a descriptive analysis of the data, then conducted correlation test and linear regression test. The relationship between both independence variables and company performance was identified to be valid.