The invention discloses a passive optical network physical layer data encryption method and a passive optical network physical layer data encryption device. The method comprises the steps: carrying out the serial-parallel conversion of physical layer data, and obtaining parallel physical layer data; performing modulation processing on the parallel physical layer data by using three modulation modes to obtain three modulation signals corresponding to the three modulation modes after modulation, wherein the three modulation modes are an 8PSK modulation mode, a 16QAM modulation mode and a 32QAM modulation mode; and based on a chaotic encryption algorithm, performing encryption processing on the three modulation signals to obtain encrypted modulation signals. According to the invention, the physical layer data is modulated in various modulation modes. The modulation signal is subjected to chaotic encryption processing, so that the data security can be effectively improved. The resource utilization rate is improved.