The present invention relates to a fused ring-containing oxazolidinone compound shown by general formula, a pharmaceutically acceptable salt thereof and a stereoisomer thereof, wherein R1, R2, R3, R4, R5, R6, A, B and C are as defined in the description. The process includes passing the heavy kerosene fraction through an adsorption separation system for separating the normal paraffins from the paraffin mixture. The truncated circular element has an orifice extending perpendicularly through the center of the truncated circular element.