COVID-19 pandemic has led to the confrontation of higher education system with enormous challenges. This necessitated the urgent transition from face-to-face teaching to online teaching. A comparative study of digital education in seven different countries was conducted. This study established grey comprehensive evaluation model based on entropy weight method, which was successfully validated by reliability test. In general, developed countries tend to have high comprehensive evaluation value while Finland, South-Korea and Latvia have relatively low grey correlation coefficient in several certain indicators, leading to a sharp drop in the overall score. Romania ranked last while China ranked second as a developing country as well. This is followed by model optimization though input-output analysis method based on the upgrading of higher education system due to the pandemic's influence. The study launched a conclusion that research and development personnel, infrastructure funds and university financial investment in digital education have relatively more obvious effects on improving the quality of higher education system. [For the full proceedings, see ED621892.]