In this paper, we describe the building of a comprehensive numerical compositional model that simulates CO2 Huff-n-Puff in an actual Middle Bakken horizontal well based on a good history match. The embedded discrete fracture model (EDFM) method was used to efficiently and easily handle hydraulic fractures that appeared in the model using non-neighboring connections. We observed that the EDFM method is faster than the traditional local grid refinement method. Therefore, we used the EDFM method to conduct our simulation studies in this Middle Bakken tight oil reservoir model. There were five sensitivity factors measured to quantify their effects on CO2 Huff-n-Puff effectiveness and the contribution of each parameter to cumulative oil production was ranked after 7000 days. CO2 diffusivity is the most important of these, followed by the number of cycles, CO2 injection time, CO2 injection rate, and CO2 soaking time. The enhanced oil recovery can reach from -1.3% to 5.9%. This study is highly meaningful and can give valuable reference to practical works conducting the CO2 Huff-n-Puff process in a Middle Bakken tight oil reservoir.