Abstract: Provided herein is a method of manufacturing a polyolefin sheet using a circulating belt and a first roller, comprising the steps of: heating polyolefin resin to melt polyolefin; and forming the molten polyolefin into a polyolefin sheet using an extruding die, wherein the circulating belt includes a plurality of second rollers (cooling rollers) which come into contact with an inner side of the circulating belt and are arranged in a circle around the circulating belt running in a circle and which cool the rotating circulating belt; a temperature of the circulating belt is maintained at 0˜30 to cool the polyolefin sheet such that the polyolefin sheet has desired thickness, a temperature of the first roller is set to a specific temperature between 40 and 120, and the temperature of the first roller is maintained in a temperature range of the specific temperature ±5; and a linear speed of the molten polyolefin sheet is substantially equal to a rotation speed of the circulating belt or the first roller to obtain a