The invention relates to a horizontal well sealing test system. The horizontal well sealing test system comprises a ground numerical control device, and further comprises coiled tubing, a coiled tubing over-liquid joint and a horizontal well test sealing instrument string which are sequentially connected and internally provided with communication lines correspondingly, and the communication linesare sequentially connected; overflowing pipes are arranged in the coiled tubing over-liquid joint and the horizontal well test sealing instrument string correspondingly and sequentially communicate; and the ground numerical control device is arranged on the ground and connected with the communication line arranged in the coiled tubing. According to the horizontal well sealing test system, tensionand magnetic positioning information of the coiled tubing and the horizontal well test sealing instrument string in the downhole sealing operation whole process is monitored in real time, and thus a safe and reliable sealing test in the sealing operation work is achieved.