The invention discloses a screening mechanism before automatic assembly of a universal-joint sleeve. The screening mechanism comprises a support frame, an enclosure wall, a turntable, a first air cylinder, a platform, an infrared detector, a second air cylinder and a conveying channel. According to the screening mechanism, the position of the universal-joint sleeve is selected by the turntable in combination with the enclosure wall, the infrared detection and the air cylinders; the enclosure wall is provided with an opening, a recovery channel which is connected to the turntable is formed at one end of the opening, a shaft sleeve which keeps a correct direction with the recovery direction of the recovery channel is connected to the outer side of the opening, and the infrared detector is arranged at the upper end of the outer side of the opening, is used for detecting whether the direction of the shaft sleeve is correct, and is connected with the air cylinders; and when the infrared detector detects that the direction of the shaft sleeve is not correct and after the air cylinder receives a signal from the infrared detector, the air cylinder is started, and the shaft sleeve is pushed by a push rod so as to be pushed back to the interior of the turntable, therefore the direction of the shaft sleeve can be fully-automatically screened, the subsequent shaft sleeve machining step is simplified, the working efficiency and effect are improved, the hand labor is lightened, and the production cost is reduced.