The invention relates to an anti-blocking device and a biological purification tank. The anti-blocking device comprises: a controller: an air source device, which is electrically connected with the controller; a plug-flow air blowing assembly, which is electrically connected with the air source device; a drainage air blowing assembly, which is electrically connected with the air source device; a first guide plate and a second guide plate, wherein the first guide plate is arranged on a pool wall and located between the plug-flow air blowing assembly and a screen, and the second guide plate is arranged on the pool wall and located between the drainage air blowing assembly and the screen; and a guide mechanism, which is arranged above the surface of the screen, and comprises a mounting base,a guide claw and a moving assembly. All the above components cooperate with each other, so impurities such as injected branches, plastic bags and hair floating in sewage can be effectively prevented from being accumulated on the screen, and thus, the problem that accumulation of the impurities leads to blockage of meshes, influences the water passing capacity of the screen and further influences the sewage treatment capacity of a biological purification tank is overcome.