Based on the characteristic of free space optical (FSO) channel and pulse position modulation (PPM) signal, by introducing turbo product code (TPC) in PPM modulation, the hardware circuit of the TPC-PPM coded modulation stucture is accomplished. Modulation gain and the code gain are tested experimentally, and it is proved that the design proposal is feasible. The experimental result indicates that under the condition that the information speed is 155.52 Mb/s, scintillation index σ2=0.1, modulation index M=4 and bit error ratio (BER) is 10-6, compared with the on-off keying (OOK) system, the PPM modulation principle prototype possessesa modulation gain of 9.03 dB and the code gain of TPC is more than 4.2 dB. The application of this module can greatly improve the performance of FSO communication system.