ABS T R A C T There is a degree of ambiguity about the specific factors of the built environment that impact people's mental health. This paper aims to examine the relations between an individual's mental health and the environmental risk factors. Drawing on clinical data and an outpatient survey from a hospital in China, 993 samples over 18 years old were available. A Boruta algorithm is deployed to determine the factors that affect people's mental health and an association rule algorithm is then introduced to ascertain the associations between risk factors. The analysis reveals the main risk environmental factors (i.e., environmental degradation and the absence of green spaces) and their coupling effects on mental health. Environmental degradation may be a key mediator in the green space-mental health relationship. Another key risk pattern is that physically unhealthy people who reside in places lacking green spaces are prone to having mental health problems. Considering the identified risks, there is a need for built environment professionals (e.g., architects and planners) to place greater emphasis on incorporating green spaces and environment management strategies into housing developments. This paper will contribute to the development of urban planning and management policies to create environments that support people's positive mental health.