The literature about how Information and Communication Technologies (ICTs) influence farmers’ adoption of sustainable agricultural technology is emerging, studies regarding the effects of particular smartphone-based digital extension services on farmers’ sustainable agricultural technology practices are limited. This study investigates the relationship between a digital extension service (“Zhe’ yang’ shi” WeChat application) and the adoption of soil testing and formula fertilization, a precision fertilization technology. A household choice model is constructed to explain the impact of the application. Based on a household-level data set from a survey of 400 farmers in Zhejiang in 2022, empirical results show that the use of the “Zhe’ yang’ shi” WeChat application significantly increases the adoption of soil testing and formula fertilization. We also discuss the heterogeneous effect by different production scales. The findings enrich the literature regarding ICTs’ influence on farmers’ behavior in adopting sustainable agricultural technology. It provides a valuable example for developing countries to promote sustainable agriculture through digital technology.