<p>The environmental disruption caused by engineering project construction conflicts with the green transformation goals of the construction industry. Encouraging contractors to adopt environmentally friendly behaviors is essential for promoting sustainability. The diffusion of green behaviors among contractors is driven by social networks and group interactions, with dynamic shifts in group behavior shaping the overall green transition process. This study applies a cellular automata (CA) model to simulate the dynamic diffusion process of green behaviors among contractors. Multi-state transformation rules are developed to compare the diffusion effects under various scenarios and to uncover the underlying mechanisms by which key factors influence the prevalence and diffusion rate of green behaviors. Contractors are categorized into four behavioral states: refusal, hesitation, acceptance, and maintenance. Those in the hesitation stage are particularly susceptible to transitioning to maintenance under the influence of both internal and external factors, with environmental attitudes playing a significant role in motivating green behavior adoption. The location and spatial distribution of contractors, the density of group states, governmental environmental policies, and individual green preferences collectively influence the diffusion process. Stochastic diffusion processes significantly accelerate behavioral adoption, while policy incentives and a higher proportion of highly motivated adopters synergistically enhance the ultimate penetration rate of green practices. This study integrates contractors’ internal conditions with external environmental influences to analyze the evolution of green behaviors. The findings provide a basis for developing intervention strategies aimed at increasing the proportion of sustained green behaviors within contractor groups and reducing the overall diffusion time, thereby enhancing the industry’s environmental performance and advancing sustainability goals.</p>