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The paper aims to deal with the numerical simulation of cavitation phenomena inside the centrifugal pump and analyze the development of cavitation based on improved cavitation model, Standard k-ε and RNG k-ε turbulence model. When cavitation flow and non cavitation flow were simulated and analyzed, the pressure of blades under incipient cavitation, developed cavitation and serious cavitation were gotten. The paper also gave the principle of incipient cavitation and divided the region into five cavitation regions based on bubble relative length. The results show that with the decreasing of inlet total pressure, bubble appears firstly in suction surface of the blade, and then moves along the blade profile, and next forms attached cavitation bubble. After this stage, bubble is gradually out of the mainstream movement and close to the pressure surface. Finally, the flow passage is filled with bubble, which hinders the flow. The number σ=0.3067 of incipient cavitation is a greater dimension hierarchy than that of σ=0.0281 under design condition. Seen from the impeller meridian plane, bubble appears firstly in the near the hub, goes towards forward cover plate, and attaches near the front cover. Cavitation in centrifugal pump is subdivided again into the five stages, that are incipient cavitation, critical cavitation, developing cavitation , complete cavitation, broken cavitation.