NOVELTY - Increasing production of light olefinic hydrocarbons from hydrocarbon feedstock by catalytic cracking, comprises feeding a stream containing 2-3C paraffinic hydrocarbons into a recycling furnace (11) where it is converted to 2-3C olefinic hydrocarbons by a thermal cracking reaction, and recycling the converted 2-3C olefinic hydrocarbons to the quenching step; and recycling a portion of the stream containing C4 plus hydrocarbon to the catalytic cracking reaction step, the catalyst regeneration step, or both steps.    USE - For increasing production of light olefinic hydrocarbons (e.g. ethylene and propylene) from hydrocarbon feedstock (i.e. naphtha or kerosene or a hydrocarbon mixture having a boiling point of 30-350degreesC) (claimed), useful in the petroleum chemical industry.    ADVANTAGE - An effective separation process structure and recycle method of light olefins are used not only to increase the productivity and efficiency of an overall process, thus effectively increasing the production of light olefins, but also to simplify the overall process. The economic efficiency of an overall process is increased, by minimizing separation processes and hydrogenation reactions.    DETAILED DESCRIPTION - Increasing production of light olefinic hydrocarbons from hydrocarbon feedstock by catalytic cracking, comprises:    (A) feeding hydrocarbon feedstock and steam into a catalytic cracking furnace where hydrocarbon feedstock is subjected to a catalytic cracking reaction in the presence of a catalyst;    (B) regenerating the catalyst used in the catalytic cracking reaction by a continuous or periodic regeneration procedure, and recycling the regenerated catalyst into the catalytic cracking furnace;    (C) quenching, compressing, and separating the product of the catalytic cracking reaction, to separate and recover each of hydrogen, methane, and 2-3C olefinic hydrocarbons and to separate into a stream containing 2-3C paraffinic hydrocarbons and a stream containing C4 plus hydrocarbons;    (D) feeding the stream containing 2-3C paraffinic hydrocarbons into a recycling furnace where it is converted to 2-3C olefinic hydrocarbons by a thermal cracking reaction, and recycling the converted 2-3C olefinic hydrocarbons to the quenching step; and    (E) recycling a portion of the stream containing C4 plus hydrocarbon to the catalytic cracking reaction step, the catalyst regeneration step, or both steps.    DESCRIPTION OF DRAWING(S) - The figure is a process diagram showing the production of light olefinic hydrocarbons from hydrocarbon feedstock by catalytic cracking.    Quench tower (2)    Splitter (4)    Low-temperature heat exchanger (5)    2C Hydrogenation reactor (9)    Recycling furnace (11)