Waste management is a key challenge the world currently faces. Solid waste imports (SWIs) are counteractive to the construction of ecological civilization. The comprehensive prohibition of “foreign waste” (FW) imports (FWIs) is an iconic measure to promote ecological civilization and ecological environment safety. Strengthening the People’s Republic of China (PRC)’s supervision of SWI (SSWIs) is an important means of implementing the comprehensive prohibition of FWIs, while existing research has paid little attention to the behaviour of SSWIs. This paper firstly analyses the influential factors of the behaviour of SSWIs based on the theory of planned behaviour (TPB), and five corresponding research hypotheses are put forward accordingly. Then, it uses 262 micro questionnaires regarding the behaviour of SSWIs in the Port of Waigaoqiao in Shanghai, PRC, and constructs a structural equation model based on the TPB to identify the influential factors and effects of the behaviour of SSWIs. Some interesting findings are observed in this research. Firstly, it indicates that attitude, subjective norms (SNs) and perceived behavioural control (PBC), all indirectly act upon supervision behaviour by influencing supervision intention. Secondly, PBC acts directly on the behaviour of SSWIs, which is consistent with the TPB. Thirdly, the direct effects on supervision intention from strongest to weakest are SNs, attitude, and PBC, respectively. The conclusion provides important policy enlightenment for the supervision optimization of the behaviour of SSWIs. The supervision intention can be motivated from various angles by strengthening the attitude, SNs and PBC of customs supervisors, subsequently strengthening their supervision intention and behaviour.