The invention discloses application of hydrocyclone separation technology in an MCP (maximizing catalytic propylene) device. The invention involves a fractionating tower, a stable reboiler, a slurry oil crude oil heat exchanger, and a hydrocyclone separator. The steps include that: slurry oil in the fractionating tower passes through a slurry oil pump to reach high temperature and high pressure, then the slurry oil flows through the stable bottom reboiler and the slurry oil crude oil heat exchanger in order, after cooling to a certain temperature, a part of slurry oil flows back to the fractionating tower through a pipeline, and the other part of slurry oil flows into a liquid inlet of the hydrocyclone separator at certain flow, and then flows into a hydrocyclone head through a clear stream pipe outer wall, and the clear stream pipe outer wall is equipped with a spiral structure, the lower end of the hydrocyclone head is funnel-shaped, after entering the lower end of the hydrocyclone head, the slurry oil undergoes high speed rotating motion, then clear and heavy slurry oil can be separated, the clear stream returns to the upper part of the hydrocyclone separator through the clear stream pipe and flows out, and returns to the fractionating tower, and the heavy stream flows out from the bottom of the hydrocyclone separator and is then thrown out of the device. The invention has the advantages of small slurry oil viscosity, low specific gravity, high solid-liquid separation efficiency, low manufacturing cost and small space occupation.