1. A human body back-scattering inspection method comprising: obtaining a back-scattering scan image of a human body under inspection; distinguishing a body image from a background image in the back-scattering scan image; and calculating a feature parameter of the background image to determine whether a radioactive substance is carried with the human body; wherein the calculating of the feature parameter of the background image to determine whether the radioactive substance is carried with the human body comprises: calculating an average luminance value of pixels in the background image; and determining that the radioactive substance is carried with the human body if the average luminance value is larger than a preset value.