The invention provides an automatic cocoon feeding device of an automatic silk reeling machine. The normal working state of a door opening and closing mechanism of the automatic cocoon feeding device is a door closed state. A door opening and closing mechanism of a cocoon outlet hopper of the automatic cocoon feeding device is driven by normal-direction rotation of a sensing rod to open a door. The normal-direction rotation of the sensing rod is driven by swing of a swing combining piece in the first direction. The swing in the first direction means that the swing piece drives a lifting mechanism to swing direction of ascending motion. The door opening and closing mechanism is driven by the reverse-direction rotation of the sensing rod to close the door. A restoration component of the sensing rod is further arranged. A delay mechanism for reverse-direction rotation of the sensing rod is further arranged, so that the swing combining piece drives the lifting mechanism to descend. In the initial period that a cocoon feeding hopper moves downward from a highest position, the sensing rod does not rotate in the reverse direction to drive the door opening and closing mechanism to close the door. The automatic cocoon feeding device is simple and reasonable in structure, and the time for opening and closing the door of the cocoon outlet hopper is accurate, so that the cocoon feeding quality is improved.