The invention discloses a method for detecting a dynamic balance fault of a multi-wheel-disc shafting of a rotary machine without trial weight. A frequency response function between vibration the bearings on the two sides of a rotor and impact forces received by journals is tested, excitation forces on the journals in the two sides are calculated according to actually measured vibration of the twobearings in the two ends of the rotor, and an unbalanced force is eliminated through dynamic balance weighting on discs at the two ends of the rotor. According to the method, dynamic balance test without trial weight is realized, and the magnitude and angle of the unbalanced force are directly detected from vibration test data; vibration in horizontal and vertical directions and coupling therebetween are considered, an influential coefficient is calculated without establishing a rotor dynamic model, and the accuracy of dynamic balanced test is higher; and the method can be used to effectivelyreduce the frequency and risk of dynamic balance test, improve the efficiency of dynamic balance test of rotary machines, and is especially suitable for dynamic balance fault detection for shafting of the rotary machine in the whole real state.