The main cause of yellow, fishy and smelly discharge 30 days after delivery is pathogenic bacterial infection, such as endometritis, bacterial vaginosis and cervicitis. 1. Endometritis: the infection of the uterine cavity can be caused by the presence of residue in the uterine cavity, etc., and the yellow, fishy and smelly discharge will be produced under the action of bacteria. 2. Bacterial vaginosis: the local anti-infective ability is weaker after delivery, which may lead to bacterial vaginitis due to retrograde infection of bacteria and other reasons. Inflammatory secretions increase, and under the action of bacteria, the problem of yellow, fishy and smelly discharge occurs. 3. Cervicitis: If there is damage to the cervix during labor, the local resistance to infection is weak after delivery. This can lead to cervicitis due to retrograde bacterial infection, which can cause yellow, fishy and smelly discharge under the action of bacteria. There are many other reasons that can lead to the phenomenon of yellow, fishy and foul-smelling discharge 30 days after delivery. It is recommended that such patients go to a regular hospital, cooperate with the doctor to complete the relevant examinations, identify the causes and actively deal with them.