The invention provides a high impact high gloss bimodal polystyrene material and preparation method thereof, comprising the following steps: (a) the solution of polybutadiene rubber component mixed with polystyrene monomers is provided; wherein, the polybutadiene rubber component is selected from high cis-polybutadiene and/or low cis-polybutadiene, the cis-content of high cis-polybutadiene is not less than 94% by mole and the cis-content of low cis-polybutadiene is between 33% to 40% by mole ; (b) the solution obtained from the step (a) is used to perform prepolymerization reaction of styrene monomers to obtain a prepolymerization solution system which does not generate phase transition; (c) the prepolymerization solution system obtained from the step (b) is used to perform further prepolymerization reaction of styrene monomers in shearing force field until the system generates phase transition to obtain rubbery state material of which the particle size presents bimodal distribution; (d) the conversion rate of styrene monomers in the material obtained from the step (c) is further increased to obtain the high impact high gloss bimodal polystyrene material. The invention also provides a preparation method of the high impact high gloss bimodal polystyrene material.