The invention provides an undesirable odor removing agent and a preparation method thereof, polyolefin plastic with low undesirable odor and a preparation method thereof. The undesirable odor removing agent is prepared from the following components in percentage by mass: 30 percent to 70 percent of cyclodextrin and 70 percent to 30 parts of zinc diricinoleate; the method for preparing the undesirable odor removing agent comprises the following steps: weighing the cyclodextrin and the zinc diricinoleate; uniformly mixing and reacting at 80 DEG C to 150 DEG C for 1h to 5h; cooling to room temperature and granulating. The polyolefin plastic with the low undesirable odor is prepared from the following components in parts by weight: 85 to 99 parts of polyolefin resin and 0.01 to 2 parts of the undesirable odor removing agent; the method for preparing the polyolefin plastic with the low undesirable odor comprises the following steps: weighing all the raw materials; uniformly mixing; melting and mixing at proper temperature and extruding and granulating. According to the undesirable odor removing agent provided by the invention, the undesirable odor can be remarkably reduced; when the undesirable odor removing agent is used for preparing plastic, the plastic with the low undesirable odor can be obtained and the original mechanical performance of the plastic is kept.