The invention discloses a movable top cover and a railway open wagon. The movable top cover comprises a left top cover and a right top cover, a driving device is arranged on the railway open wagon, and the driving device can drive the left top cover and the right top cover to open or close the top of a cargo compartment of the open wagon . Side beams of the movable top cover are provided with a flexible device, and the flexible device can cover gaps between the side beams and side walls. During the turning-over and unloading operation of the open wagon, the car dumper pressing machine is gradually close to the top of the side walls of the cargo compartment from top to bottom, and firstly makes contact with the flexible device, the flexible device is extruded and deformed by the car dumperpressing machine and retracts into the cargo compartment, and then the car dumper pressing machine continues to move downwards to tightly hold the top of the cargo compartment, and finally conducts the turn-over and unloading operation; in addition, after the open wagon is turned over a certain angle in the width direction, scattered particles move under the action of gravity and brush the flexible device, and the flexible device is stressed to deform towards the outer side of the cargo compartment, so that the gaps between the side beams of the movable top cover and the side walls of the cargo compartment are opened, the scattered particles can flow out of the gaps, thus completing the unloading.