The invention provides a height adjustment device of a power construction hoop, and discloses a device which is clamped onto a wire rod and fixed on the hoop and is used for adjusting the height of the hoop by motion of a hydraulic post. A fastening bolt on the hoop is not needed to be screwed, the device is more convenient to use, frequent hoop knocking is not needed, the device is simpler to operate, and labor consumption of a worker is relatively small. The device is characterized in that two fixing plates are respectively arranged at two ends of an arc clamping plate, wherein installationholes are formed in the fixed plate, a rubber cushion is arranged in the arc clamping plate, a connection plate is arranged at an outer side of the arc clamping plate, the bottom of the hydraulic postis arranged on the connection plate and is arranged at a middle position of the arc clamping plate, a middle part of the support plate is arranged on one end of a piston rod of the hydraulic post, one end of each of two hollow rods is arranged on the connection plate and is arranged at each of two sides of the hydraulic post, one end of a guide rod is arranged in the hollow rods in a sliding way,the other end of the guide rod is connected with the bottom of the support plate, an arc groove is formed in a front side of the support plate, and two sliding grooves are formed in a rear side of the support plate.