The invention provides a method of prolonging operating time of an OCT (olefins conversion technology) reactor in an OCU (olefins conversion unit). The method comprises the steps of performing hydrogenation reduction on mixed C4 olefin to form a hydrogenated product, performing purification and heating pretreatment sequentially on the hydrogenated product to form a pretreatment product, and conveying the pretreatment product and ethylene into the OCT reactor for disproportionation reaction to form a disproportionation product, wherein a butadiene content in the hydrogenated product is less than 5ppm. A content of 1-butylene in an inlet pipeline of the OCT reactor is reduced by controlling the butadiene content in the hydrogenated product to be less than 5ppm; an isomerization reaction andan inlet temperature of the OCT reactor are further reduced; an initial operation temperature of a catalyst lower; and shortening of a service life of the catalyst due to heat fluctuation is avoided,so that an operating cycle of the single OCT reactor can reach about 400-600 days, and is much greater than designed 14-30 days.