Hume's philosophy firmly implemented the principle of experience and the principle of suspicion, remarkably, he doubted the authority of rationality and explored the limitation of cognition ability based on human natural instincts such as custom, emotion and belief. Custom is a very important concept in Hume's humanity philosophy and plays a key role in the construction of Hume's epistemology. In Hume's works, we can easily discover that custom, as a kind of human nature, shows sensible characteristics and plays a leading role in causal inference so that the inference of cause and effect takes on probability instead of absolute necessity, which pushes emotion and feeling to the principal position and which shows a perceptual empirical inference line.