The development of mangrove forest environmental services plays a crucial role in human health, economic development, and the security of countries worldwide. This study aims to establish and validate a model for assessing the factors influencing the willingness-to-pay for mangrove forest environmental services. The proposed model comprises four key factors: attitude, subjective norm, perceived behavior control, and environmental knowledge. Data were collected by surveying 235 individuals from various households in Phu Long commune, Vietnam. The Partial Least Squares—Structural Equation Modeling (PLS-SEM) methodology was employed for data analysis. The research findings reveal that perceived behavior control significantly impacted residents’ willingness-to-pay, followed by attitude, environmental knowledge, and subjective norms. Furthermore, certain demographic characteristics such as gender and family size mediate the relationship between independent and dependent variables. Based on the obtained results, several policy recommendations are put forward.