The invention relates to a ball-cage-type universal shaft of a screw drill. The ball-cage-type universal shaft of the screw drill is used for linkage and power transmission of the screw drill. Outer sleeve connectors at the two ends of the screw drill are connected with a transmission shaft and a rotor of the screw drill respectively. Each outer sleeve connector is connected with a middle shaft through a steel ball inside a retaining frame. The end portion of each outer sleeve connector is provided with a sealing cover, and the end portion of each sealing cover is provided with a clamping cover. A clamping ring and a safe pulling device are sequentially arranged between each sealing cover and the corresponding retaining frame. Shock-absorbing devices are arranged on the connection portions of the outer sleeve connectors and the middle shaft. The ball-cage-type universal shaft is good in shock-absorption and sealing performance and high in high-temperature resistance, high-pressure resistance and abrasion resistance, the service life is greatly prolonged, and the ball-cage-type universal shaft can normally work in the environment with high pressure of 7 atm or 0.7 MPa at a high temperature of 180 DEG C, can continuously safely run for more than 400 hours underground in a failure-free state, is strong in underground operation adaptation ability, convenient to install and adjust, quick, easy and convenient to disassemble and assemble and capable of effectively shortening maintenance and replacement time and improves drilling efficiency.