The present invention relates to a catalyst for epoxidation of an olefin. The catalyst is a modified titanium silica molecular sieve, the pore size is 10-30 nm, the content of TiO is 0.5-10 wt%, the pore volume is 1.0-1.5 mL / g, the aperture distribution rate is >=93.5%, and the specific surface area is 150-500 m<2> / g. A preparation method comprises the following steps: a template agent, a template modifier, water and a solvent are added into a reactor, heating under stirring is conducted, then a silicon source is added, and thermal insulation, suction filtration and drying are conducted to obtain a molecular sieve raw powder; the molecular sieve raw powder, an extrusion aid, an adhesive agent and a glue mixing agent are mixed evenly, an obtained mixture is subjected to extrusion molding, and then drying and roasting are conducted to obtain a molded molecular sieve; a titanium source is added into the molded molecular sieve to prepare the titanium silica molecular sieve, and finally a surface modifier is added for modificationto obtain the catalyst. The catalyst provided by the present invention is suitable for catalyzing the oxidation of propylene with cumyl hydroperoxide. The conversion rate of cumyl hydroperoxide is high, the selectivity of propylene oxide is high and the content of a byproduct, namely phenol is relatively little.