The invention provides polystyrene butene diacid dimethyl ester and a preparation method therefor and application thereof. The preparation method comprises the step of carrying out polymerization reaction on styrene and butene diacid dimethyl ester, which serve as reaction monomers, in the presence of polyethylene glycol and azodiisobutyronitrile in a manner of taking water as a dispersion medium, thereby obtaining the polystyrene butene diacid dimethyl ester. The invention also provides the polystyrene butene diacid dimethyl ester prepared by the preparation method, application of the polystyrene butene diacid dimethyl ester in preparation of tracers for monitoring oil-producing profiles of horizontal wells and the polystyrene butene diacid dimethyl ester containing tracers for monitoring the oil-producing profiles of the horizontal wells. The polystyrene butene diacid dimethyl ester provided by the invention can be completely dissolved in crude oil, and by using the polystyrene butene diacid dimethyl ester to monitor the oil-producing situation of each segment after multistage fracturing of the horizontal wells, the aims of analyzing the oil-producing situation of each segment and drawing the liquid oil producing profile of each segment can be achieved.