The invention relates to an oil-gas-water multi-phase flow adjusting apparatus, which mainly comprises an inlet accelerating pipe section, a vortex flow guide spiral pipe, a gas circuit exit connection pipe section, a liquid receiving cone, a mixed liquid relief exit connection pipe section and a sampler exit connection pipe section, and which has the function for changing at intervals the flow pattern, the flow state and the components of the oil-gas-water multi-phase flow. The invention also relates to an oil-gas-water multi-phase flow rate measuring apparatus and its measuring method. The measuring apparatus comprises a blind three-way mixing means, a pressure differential type flow measuring device, a single-γ phase volume fraction meter, a dual-γ phase volume fraction meter, an oil-gas-water multi-phase flow adjusting apparatus and a computing system. The measuring method is as follows: the single-γ phase volume fraction meter and the dual-γ phase volume fraction meter measure the gas content GVF and the water content WC respectively; the pressure differential type flow measuring device measures the differential pressure ΔP of the total flow rate; the computing unit computes the oil flow rate Qo, the gas flow rate Qg and the water flow rate Qw.