Abstract: The ocean internal wave has an important influence on sound propagation and underwater acoustic detection.The characteristic parameters and the spectrums of internal waves are analyzed extracted from the ocean environment measurements of a shallow-water experiment conducted in the northern South China Sea.The Monte Carlo method is applied to investigate the influences of the random linear internal waves on Transmission Loss(TL)in the shallow water.The influence mechanism of the relative position of the source and the thermocline on the fluctuation is explained by the ray theory.It is shown that maximal probabilities of the TLs are increased,and the probability distributions of TLs are more dispersive with the increase of the source frequency,the average energy flow density of linear internal waves and the ranges.When the source is located below the thermocline,the probability distributions of TLs are more dispersive than the case that the source is located above the thermocline.The cumulative effect of the linear internal waves is more significant with the increase of the ranges.The TL probability of TLs can be increased by 8 dB at 40 km when the source is located below the thermocline.Sound rays pass through the thermocline more easily in a thermocline environment when the internal waves are disturbed.