The utility model discloses an online ovality detection device of a continuous pipe, which is designed for compacting the structure of a continuous pipe detection device and increasing the ovality detection accuracy of the continuous pipe. The online ovality detection device mainly comprises an inner cylinder, an outer cylinder, a diameter expanding rod, a vortex displacement sensor, fixed rollers, a fixed plate, a floating roller, a rotary coder and the like, wherein the inner cylinder and the outer cylinder are composed of upper and lower half cylinders; the diameter expanding rod is connected to a wearable head, sleeved with a compression spring and arranged on the inner cylinder; the vortex displacement sensor is aligned to the tail end of the diameter expanding rod and arranged on the outer cylinder; the fixed rollers are fixed on two side surfaces of the outer cylinder; the fixed plate is connected to the outer wall of the bottom end of the outer cylinder; and the floating roller and the rotary coder are arranged on the fixed plate. According to the utility model, the circumferential arrangement space of the vortex displacement sensor is increased by utilizing the diameter expanding rod of the continuous pipe; therefore, arrangement of the sensor is more compact; the ovality detection result is more accurate; equipment is more convenient to install and use; the data read is more direct; when the continuous pipe works, the detection device is capable of online detecting the ovality of various sections of the continuous pipe in real time with no influence on an operation machine, thus important basis is provided for judging the performance indexes and service life of the continuous pipe.