A large-caliber excrement falling door mechanism for an automatic bed toilet and translatable under the driving of a patient is provided. The minimum dimension of the excrement falling door is not less than the width dimension of the outer edge of the loop of a toilet, so the excrement falling door has a large caliber. The excrement falling door is translatable under the driving of the patient bya driving plate so as to expand the excrement receiving range of a toilet bowl. The patient translates the entire bed toilet by the driving plate, which reduces the restriction on the position of thepatient while ensuring effective reduction of pollution. The patient is not required to be aligned with an excrement falling hole when defecating so as to be comfortable. The two measures greatly reduce the chance that the automatic bed toilet being is contaminated by the excrement. The excrement falling door is the key mechanism of the automatic bed toilet.