The invention provides a large mechanical equipment structure dynamic similarity test method, comprising the steps as follows: (1) a basic similarity theorem is adopted, all physical quantities are listed, geometrical quantity, density and elastic modulus are determined as basic physical quantities, and the similarity theorem is written into a dimensionless equation expressed by the basic physical quantity; (2) according to concerned basic physical principle, the similarity ratio of all physical quantities adopts similar relation expression, and the similar relation expression is modified according to a structure elastic vibration similarity equation; (3) similar model material is selected, density similarity ratio and elastic modulus similarity ratio are determined, geometrical quantity similarity ratio is determined, and the similar model design is then completed; (4) a structure dynamic test of the similar model is carried out so as to obtain the dynamic characteristic number which is substituted into the similarity relation expression so as to work out the dynamic characteristic data of the original model which is also the natural vibration frequency. The large mechanical equipment structure dynamic similarity test method realizes the conversion of ultra-large structure dynamic natural frequency with small model, effectively reduces the scales of dynamic test objects, simplifies the test instruments, and reduces the test cost.