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, so as to improve flexibility of a system and satisfy a requirement that an error probability is reduced as low as possible. 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 non-zeros is the same as the number of zeros, and in a delimiter sequence, the number of non-zeros on odd bits is equal to the number of zeros on even bits, and the number of non-zeros on even bits is equal to the number of zeros on odd bits, 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 number of zeros in a continuous zero group is X, the 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.