The invention provides a thermal insulating device based on a petroleum liquid nitrogen pipeline. The thermal insulating device comprises a protection shell A, a rectangular tank, and a circular holeB, the protection shell A is formed by welding a semi-circular shell A and two rectangular plates A, the two rectangular plates A are welded to the left and right ends of the outer wall of the semi-circular shell A symmetrically, and a semi-circular plate A, a semi-circular plate B, a semi-circular clamp, a semi-circular clamping plate, a rubber cushion and a thermal insulating layer are arrangedon each of a semi-circular shell B and the semi-circular shell A. According to the thermal insulating device, because of mutual matching of the semi-circular plates A and the semi-circular plates B with semi-circular grooves A, semi-circular grooves B, semi-circular grooves C, and semi-circular grooves D, on the one hand, air leaking can be prevented at the connection through matching of the semi-circular plates A, the semi-circular grooves A and the semi-circular grooves C, and on the other hand, through matching of the semi-circular plates B, the semi-circular grooves B and the semi-circulargrooves D, the two thermal insulating devices can be prevented from being disconnected due to the outer force action after connecting of the two thermal insulating devices while the thermal insulating effect is enhanced.