This a detailed paper of Mr. Gautam and Mr. Panda of Iffco Phupur about the case that a rotor of a centrifugal CO2 compressor rotates reverse. A centrifugal machine experiences reverse torque due to reverse flow of high pressure fluid from discharge to suction side through the rotor as soon as the machine is tripped at full load. But reverse rotation is an unwanted phenomenon as it is always associated with severe radial vibration and axial displacement of the rotor which may lead to damage of the bearings and rubbing of seals with the stationary components. This paper describes how the reverse rotation of CO2 compressor trains provided in phase-II urea plants at Phulpur was diagnosed by the analysis of post trip data picked up by Data Manager-2000 and step by step in house approach to find the solution.