A process of producing isopropyl benzene which solves the problem of high amount of n-propyl benzene according to the prior art. The process separates the polyisopropyl benzene through a suitable rectification into two streams of relatively lighter and heavier components, wherein the content of diisopropylbenzene in the stream of relatively lighter components is controlled to be at least greater than 95 wt %, and the content of tri-isopropyl benzene in the stream of relatively heavier components is controlled to be at least greater than 0.5 wt %. Such a technical solution subjecting the two streams respectively to the transalkylation solves the problem raised from the prior art, and is useful for the industrial production of isopropyl benzene.