We evaluate the link gains of the ultraviolet non-line-of-sight model under different altitudes based on the Monte Carlo ray tracing method. We first evaluate the scattering and attenuation coefficients under different altitudes. Then, we evaluate the link gain of the small and large transmitting-receiving angles. The bit error rate (BER) performance is evaluated assuming on-off keying (OOK) modulation and the maximum likelihood (ML) detection. We consider the mixed Gaussian distribution (MGD) of the PMT received signal. Finally we investigate the maximum transmission rates under different altitudes with respect to the communication distance.