A dog vomiting black liquid may be caused by anthrax infection, or it may be caused by canine distemper virus or parvovirus, so it is best to take the dog to the pet hospital for examination and treatment as soon as possible to avoid delaying the condition. If it is anthrax, the dog needs to be isolated and treated immediately. Protective measures must be worn when coming into contact with the dog. Wash hands and disinfect in time after contact to avoid infecting humans.