A method for producing propylene by using Fischer Tropsch synthetic oil in catalytic cracking mode includes steps that: material flow rich in small molecular olefins and Fischer Tropsch synthetic oil raw materials are mixed and injected into a reactor to be contacted with a catalytic cracking catalyst containing shape-selecting zeolite with average pore size smaller than 0.7 nanometer for reaction, reaction oil gas and the catalyst with carbon depositing after reaction are led into a settler for gas-solid separation after the reaction is finished, the separated oil gas is separated through a follow-up separating system to obtain dry gas, liquefied gas containing propylene, gasoline diesel oil fractions and the like and is further separated to obtain propylene; and the separated catalyst with carbon depositing is performed with steam stripping and scorching and then returns to the reactor for recycling. The method for producing propylene by using Fischer Tropsch synthetic oil in catalytic cracking mode can be used for processing heavy Fischer Tropsch synthetic oil fractions and processing light Fischer Tropsch synthetic oil fractions. Under the same reaction conditions, the method is used for processing Fischer Tropsch synthetic oil, yield of propylene is improved by 6.74%.