The invention provides an uplink transmission method for an OFDMA-PON (Orthogonal Frequency Division Multiplexing Access-Passive Optical Network) system with low resource cost. The uplink transmission method of the system is based on single sub-carrier modulated Gold sequences. ONUs (Optical Network Units) mounted in the PON (Passive Optical Network) system modulate different Gold sequences on a same distance measurement carrier, thereby distinguishing different ONUs. The good self-correlation characteristics of the Gold sequences are utilized at an OLT (Optical Line Terminal) end. Correlation operation is carried out on received uplink OFDM signals and natively stored ONU signals, thereby obtaining relative position information among the ONUs. The lengths of the Gold sequences are determined by the number of the ONUs. The CPs (Cyclic Prefixes) on the Gold sequences are set as zero. In order to simplify the calculation complexity of correlation operation, on the basis of the condition that the OFDMA-PON uplink is relatively stable, the OFDM signal word lengths participating in the correlation operation are optimized. According to the method, the logic complexity of the symbol synchronization of the OFDMA-PON uplink is greatly reduced.