Similarity is a widely used concept in cognition. There are general similarity application and application of similarity in the figurative thinking. Similar and similarity surplus are a pair of chief categories of figurative thinking. Similarity surplus contains:the different images of two things;like-but-not-quite-alike phynomenon observed when the forms of two things are compared;the part unobserved of two things. The similarity between two things may or may not indicate their identity. When the similarity of two things does not depend on the degree of the similarity of the whole of two things,we must see if there is similarity surplus. The inconsistence of the degrees of identity and of similarity is the cause for wrong judgements,and the trap in thinking for you to be fooled and deceived by taking a fake as genuine. The functions of similar and similarity surplus can also be transferred to creative thinking.