An experiment of measuring surface tension of water droplets based on pendant drop method is developed by using a smartphone and Matlab software that can be used at home. The surface tension coefficient is calculated by taking a photo of water droplets with a smartphone and then using Matlab to recognize and calculate the edges. For various clarity cases, appropriate analysis and processing methods are presented, and testing results show that the method is stable and trustworthy. It is a typical case of post-epidemic experimental teaching of university physics at home.