The behavioral intention of tourists to protect the environment is a popular topic in tourism geography research. Understanding the mechanisms that influence the post-tour behavioral intentions of heritage site visitors can effectively promote the generation of positive behavioral intentions for the sustainable development of heritage sites. Starting from the “cognitive–emotional–behavioral” path of attitude theory, we introduced environmental knowledge awareness (EKA), geomorphological value perception (GVP), place attachment (PA) and behavioral intention (BI) variables to construct a model of the influence mechanism of tourists’ behavioral intentions towards conservation in heritage sites; we test this model on the Libo World Natural Heritage Site, a karst in southern China, as an example. The results show the following: (1) environmental knowledge awareness (EKA) is the basis of place attachment (PA) and behavioral intention (BI), and place attachment (PA) plays an influential mediating role. (2) Geomorphological value perception (GVP) has a positive effect on behavioral intention. (3) The “GEPB” conceptual model fits the “cognitive–emotional response–behavioral intention” chain of tourists in natural world heritage sites and passes the empirical test; (4) The direct positive effect of place attachment on behavioral intention is significant as an essential emotional factor that promotes behavioral intention. This study provides an empirical foundation for the synergistic development of conservation and tourism in World Heritage Karst Sites. It also discusses theoretical and managerial implications based on the findings and provides directions for future research.