The scintillation caused by the atmosphere turbulence and strong background noise from sunlight and other lighting equipment are two main problems in visible light communication (VLC) atmosphere transmission system. In order to overcome the channel fading effect caused by the atmosphere turbulence and the noise interference caused by the strong background light, VLC atmosphere channel with strong background noise is modeled. Diversity receiving technologies are utilized to improve the bit error rate (BER) performance of the system at the same transmitting power. According to the channel model, outdoor long-distance VLC system based on intensity detection pulse position modulation (PPM) in turbulence atmosphere channel using diversity receiving technologies is finally set up. In our simulation, the system bandwidth is 400 MHz and bit rate is 800 Mb/s. The BER performances of three diversity receiving technologies: maximal ratio combing (MRC), equal gain combing (EGC), selection combing (SC) are also compared. The results show that under the same transmitting power, the improvement of BER performance by MRC is the best, followed by EGC and SC is poor. Taking 7% forward error correction(FEC) as the BER threshold, the required LED transmitting power is greatly decreased with MRC. Furthermore, with the increase of the number of diversity branches, the BER performance is better.