The invention provides a nonfluorescent oil-base magnetic suspension for magnetic powder flaw detection and a preparation method of the nonfluorescent oil-base magnetic suspension. The nonfluorescent oil-base magnetic suspension for magnetic powder flaw detection comprises the following components in parts by weight: 100-200 parts of transformer oil, 750-900 parts of tasteless kerosene and 0.1-0.3 part of nonfluorescent photo magnetic powder. The magnetic powder is added into1-3 times of the tasteless kerosene according to the weight part for stirring into uniform paste, and the residual transformer oil and the tasteless kerosene are added for uniform stirring to obtain the nonfluorescent oil-base magnetic suspension. According to the nonfluorescent oil-base magnetic suspension, an antirusting agent and a deforming agent do not needed to be added; the nonfluorescent oil-base magnetic suspension is unlikely to rust and cannot generate foams due to stirring. Within a relatively long time period, the usability cannot be changed; furthermore, the nonfluorescent oil-base magnetic suspension is high in safety and reliability in a use process.