The invention discloses trench bottom levelling device and method, and belongs to the field of pipelines. The trench bottom levelling device comprises a walking mechanism, a power control system, a planing and milling piece and a levelling assembly. The walking mechanism is used for moving along a trench bottom of a pipe trench. The planning and milling piece is connected with the back end of thepower control system and is used for planning the trench bottom to the preset depth and then milling to be smooth. The levelling assembly is used for acquiring height data of the planning and millingpiece and transmitting the height data to the power control system. The power control system is arranged on the walking mechanism and is used for providing a drive force for the walking mechanism andthe planning and milling piece and controlling the planning and milling piece to move up and down according to the height data. The trench bottom levelling device can be used for milling the trench bottom to be smooth, so that the follow-up pipeline construction operation is ensured to be smoothly carried out; and in addition, by using the device for operation, the working efficiency is high, andthe trench bottom can be leveled without the need of more work by working personnel, so that the labor intensity of the working personnel is effectively reduced.