The invention provides a control method of a washing and drying all-in-one machine, a control device for the washing and drying all-in-one machine, and the washing and drying all-in-one machine. The control method comprises the following steps: acquiring initial washing and drying time of the washing and drying all-in-one machine in a washing and drying process; in the washing and drying process,carrying out countdown on the initial washing and drying time to obtain the remaining washing and drying time; acquiring a weight of a load in a washing drum of the washing and drying all-in-one machine; according to the weight of the load, determining whether the remaining washing and drying time needs to be adjusted or not; if so, adjusting the remaining washing and drying time; displaying the remaining washing and drying time. By adopting the technical scheme provided by the invention, the remaining washing and drying time can be adjusted according to the actual amount of the load which isput into the machine by a user, and the corresponding display is performed; the problems that when the load is heavier, the phenomenon that the time display is easily finished, but the load is not dried is easily caused, and when the load is lighter, the phenomenon that the load is dried, but the drying action is still not finished, and the display time is still in progress is easily caused can besolved; the drying effect is improved, the display time is more accurate, and the washing and drying all-in-one machine is more intelligent.