The present invention relates to the Passive Optical Network (PON) technology, and a method for sending an upstream transfer frame in a PON is provided. The method includes: after success of link, sending a preamble according to an allocated time slot, sending a burst synchronization delimiter, and then sending successively a burst header, a Gigabit-Capable Passive Optical Network (GPON) Transmission Convergence (GTC) frame header, and GTC frame data. In the sent synchronization delimiter, the number of zeros on the odd bits is N, the number of non-zeros on the odd bits is M, a relation |N−M|≦1 is satisfied, the max number of zeros in a continuous zero group is X, the max number of non-zeros in a continuous nonzero group is Y, and a relation |X−Y|≦1 is satisfied. A device for sending an upstream transfer frame in a passive optical network is further provided.