The growth of digital economy and sustainable development of environment are important issues related to high-quality economic development in the new era. This paper selects the yearly data of China from 2007 to 2021, constructs the China’s Environmental Performance Index, and establishes the TVP-VAR model to investigate the dynamic time-varying relationship between digital economy growth, CO2 emissions, and sustainable development of environment in short, medium and long-term. The results show that the relationships among them are time-varying at all terms. Specifically, in first, the growth of the digital economy exerts a negative impulse on CO2 emissions, and the short-term effect is greater than the long-term effect. Secondly, there exist positive impulses between the growth of the digital economy and sustainable development of environment. And CO2 emissions has a negative impact on sustainable development of environment. Thirdly, they have same influencing tendencies at certain time points, but different impact degrees. The impact of the digital economy development on environmental sustainable development has significantly increased since the COVID-19 outbreak. Therefore, the development of digital economy can effectively reduce CO2 emissions and promote the sustainable development of the environment.