By aiming the problems that in the prior art, when a weeding machine and a seeding machine are in parallel arrangement, the seed germination is influenced, so that partial regions have no seedlings, the invention provides an automatic weeding and seeding device. A single chip microcomputer control module is connected with a data processing module and then aquires ground weed density information collected by an image acquisition module; the single chip microcomputer control module controls the rotating speed of an electric motor so as to control the movement speed of a machine frame provided with a mist spraying machine and a seeding machine to decelerate along with the weed density increase, so that the mist spraying machine increases the mist spraying quantity along with the ground weed density increase; next, the seeding quantity of the seeding machine increases along with the mist spraying quantity increase together with the movement speed deceleration of the machine frame. The influence of a weedicide on the seed gemmation can be reduced; the occurrence of no seedling condition in regions with excessive weedicides can be prevented.