The utility model relates to an inner pipe post rotating joint of a sidetrack horizontal well for the completion of the sidetrack horizontal well, which comprises an upper joint, sealing rings, ball bearings, a press cap and a lower joint, wherein the connection of the upper joint and the lower joint is provided with semicircular grooves and the sealing rings, the upper joint is connected with the lower joint by inlaying two groups of ball bearings, the press cap is welded on to the upper joint, and the ball bearings are inlaid in the semicircular grooves of the upper joint and the lower joint. The utility model solves the problems in the prior art that when a well pipe post is fallen, the well pipe post needs to be forcibly fallen in most cases, so that a sleeve pipe, particularly a sieve pipe is deformed and damaged in advance, and a sleeve pipe string is damaged. The utility model can be widely used for the completion of the sidetrack horizontal well.