Method for producing ethylene and propylene by catalytic cracking

The invention provides a method for producing ethylene and propylene by catalytic cracking. The method comprises the steps: introducing an alkene raw material into a fixed bed reactor to contact the alkene raw material with a catalyst to perform a catalytic cracking reaction under the conditions of a temperature of between 500 and 680 DEG C, a pressure of between 0 and 0.5MPa, a weight space velocity of between 10 and 50h and a water-oil weight ratio of between 0 and 1.0; and separating resulting the hydrocarbon mixture obtained after the reaction to obtain the ethylene and the propylene,wherein based on the total weight of the catalyst, the catalyst contains 20 to 40 percent by weight of modified molecular sieve and 60 to 80 percent by weight of heat resisting inorganic oxide, the average grain size of the modified molecular sieve is between 10 and 100nm and the modified element is one of phosphorus and metals in the IB group or the modified elements are a mixture of elements selected from phosphorus and metals in the IB group; and based on the total weight of the molecular sieve, the content of the modified element is between 1 to 10 percent. The method provided by the invention has higher alkene conversion rate and once-through yield of the ethylene and the propylene.