High-quality development is the goal of the collaborative development of vocational education and open education, and this paper constructs a quality evaluation index system for collaborative development starting from the characteristics of vocational education and open education. The subjective and objective weights of each index are obtained by using the G1 method and the CRITIC method, respectively. The combined weights are solved by multiplicative normalization, and the synergistic development of vocational education and open education is comprehensively evaluated based on the gray correlation degree. To verify the effectiveness of the evaluation index system and explore the mechanism of synergistic development, an empirical analysis was conducted. The results show that the weight of the open education index is 0.3491, the correlation coefficient of the evaluation indexes is more than 0.7, and the factor with the strongest influence is the influence of education with a correlation value of 0.973, which indicates that the mechanism of collaborative development between vocational education and open education needs to pay attention to the influence of education, so as to promote the high-quality development of both of them.