The invention belongs to the technical field of synthesis of pharmaceutical intermediates, and discloses a preparation method of 6-cyclohexano-3,4-cyclohexyl-5-N-hexanolactam-4-ene. The preparation method comprises the following processes: firstly putting a previous batch of mother liquid containing quantitative cyclohexanone, a target product, an intermediate component and an inert solvent and a washing liquid into a reactor, starting stirring, heating to 135-145 DEG C, carrying out reflux dehydration, separating water in a dehydrater, further adding a certain amount of urea in a certain time by virtue of a special sealed device, after the addition of urea is completed, further dehydrating until a theoretical amount, stopping heating, carrying out induced crystallization, slowly cooling to room temperature, carrying out solid-liquid separation, washing a filter cake with a consumption amount of cyclohexanone, directly putting the filter cake into a next-step hydrolysis process without drying and feeding the mother liquid and washing liquid into the next batch of synthesis reaction. The process has the advantages of no need of addition of a catalyst, mild reaction conditions, no wastewater, safety and environment friendliness, energy conservation, consumption reduction, high yield, good quality and low cost and can be used for industrial production.