The present invention provides a method and an electronic apparatus for transmitting a packet with changeable spreading factor. The method comprises: utilizing a spreading circuit to select a spreading factor from a plurality of spreading factors according to a transmitting condition to adjust a spreading for the packet; and transmitting the packet. The electronic apparatus comprises: a spreading circuit and a transmitting circuit. The spreading circuit is utilized for selecting a spreading factor from a plurality of spreading factors according to a transmitting condition to adjust the spreading for the packet. The transmitting circuit is coupled to the spreading circuit, and utilized for transmitting the packet.