The space-time block coding (STBC) has the property of diversity gain in the visible light multiple-input multiple-output (MIMO) communications. However, its validity is low. And the spectrum efficiency is improved in the spatial modulation (SM) coding while the reliability was poor. Therefore, based on the advantages of STBC and SM coding, a STBC-SM concatenated coding was investigated in the visible light MIMO communications. A visible light indoor transmission channel model was established as Lambertian light attenuated. The validity and reliability of the system was verified. Simulation results indicate that the reliability of the STBC-SM concatenated coding is 5-8 dB more than SM under the precondition of ensuring the original validity and the same error rate, and on the premise of ensuring the original reliability, the efficiency of STBC-SM concatenated coding is higher than that of STBC. It shows that the concatenaed codes designed in this paper can effectively settle the contradiction between validity and reliability in the communication system, and has a good theoretical significance for researching indoor visible MIMO communication.