Abstract: Born's rule is one of the basic assumptions of quantum mechanics. It establishes a direct correspon- dence between the mathematical form of quantum mechanics and experimental measurement. However，some gener-alized quantum theories have proposed amendments to Born's rule， allowing the existence of multi - order interference terms. Recently，many researchers have tested Born's rule on different experimental systems，and the results obtained are consistent with Born's rule predictions within the error. This article introduces the methods of Born rule in optical and spin systems，and then proposes an improved method in spin system from the perspective of changing the observable. We hope that it is helpful for the understanding and research of Born rules in the future.

Key words: quantum mechanics, Born rule, three-slit interference, spin system