Abstract: This article logically analyzes the classical structural Gettier cases，famously known as ‘from false premises to obtain justified true belief via logic deduction’.Through a detailed formal analysis of several classical Gettier cases，it is concluded that during the process of applying a valid deductive inference，if what the premises express is strictly stronger than what the conclusion expresses，then there always exists a situation where at least one Gettier case happens.The fundamental reason under this result is the conservative property of deduction.

Key words: Traditional view of knowledge, Gettier cases, Deduction, Conservative Property