A clamp-type line post insulator is disclosed. The clamp-type line insulator is provided with a thread clamping device, and comprises: a body, a cable clamp, an insulation unit and an adjustable fixing unit. In the present invention, the body comprises: a receiving recess, a fixing base and a cable groove. Moreover, a pivoting end of the cable clamp pivotally connected to a pivot member that is formed on the fixing base. Particularly, after placing an electrical cable in the cable groove, the cable clamp is rotated by taking the pivot member as an axle center, thereby inserting an engaging end of the cable clamp into the engagement groove to engage with it. By such arrangements, the electrical cable be pressed and fixed in the cable groove by rotating the adjustable fixing unit.