An upstream date transmission method from optical network units (ONUs) to the optical line terminal (OLT) based on wavelet packet multi-level orthogonal coding in passive optical networks (PON) is proposed and studied. Each ONU can be assigned a special coding based on the wavelet packet coding method to share a wavelength. As the wavelet packet coding method is used, the number of ONU can be very large. And there are no need for the burst mode transmitter/receiver module and multi-wavelength lasers. So the proposed system has the advantages of low cost, high data transmission rate and large access number. This upstream system architecture model is established and simulated at the transmission rate of 1.25 Gb/s and 10 Gb/s. Simulation results show 32 ONUs, where each ONU is with a data rate of 10 Gb/s, and the total transmission rate is up to 320 Gb/s.