The evaluation of the actual drilling trajectory’s conformity to the designed wellbore trajectory during drilling operations is crucial for the smooth conduct of subsequent operations and the evaluation of drilling operation efficiency. Currently, the evaluation of the actual drilling trajectory only considers whether it hits the target and whether it reaches the intended depth, with a single evaluation indicator and no quantitative evaluation. It has not yet been combined with the actual drilling inclination data to quantitatively evaluate the degree of conformity between the actual drilling trajectory and the designed wellbore trajectory. This paper considers the wellhead, target point, end point, and inclination critical points comprehensively, innovates the concepts of wellhead deviation, target point deviation, end point deviation, and other points deviation, and provides quantitative calculation methods. It establishes the actual drilling trajectory deviation and provides a quantitative model. Taking A oilfield as an example, the model calculates the trajectory deviation of XX well as 0.478, and the trajectory deviation of YY well as 0.1, compared with XX well, YY well’s actual drilling trajectory is more consistent with the designed trajectory. The quantitative model of drilling trajectory similarity proposed in this paper provides reference for the quantitative evaluation of the similarity between the actual drilling trajectory and the designed trajectory at all sections or any section of the well, and provides theoretical basis for evaluating the drilling operation efficiency of the construction team.