A method and device for automatic film expansion and a storage medium are provided. The method includes the following. Perform overall stretching on an expanded film. An interval between each two adjacent LED wafers on the expanded film is monitored in real time. When an interval between two adjacent LED wafers on the expanded film is greater than or equal to a preset target interval, stop performing overall stretching, and search the expanded film for a local region where an absolute difference between an interval between two adjacent LED wafers and the preset target interval is greater than a preset error threshold. When the local region exists on the expanded film, perform local stretching on the local region until an absolute difference between an interval between each two adjacent LED wafers in the local region and the preset target interval is less than or equal to the preset error threshold.