High-speed rail (HSR) has gradually become a popular travel option, and passengers have high demand for streaming media services during HSR travel. However, in high-speed mobile scenarios, user bandwidth jitter is severe, and user media experience cannot be guaranteed. To this end, a cross-layer optimization method for adaptive cloud collaborative transmission of streaming media, based on DASH protocol, is proposed in this study. Firstly, a cross-layer architecture for adaptive cloud cooperative transmission of streaming media, based on DASH protocol, is proposed, and a QoE model for users in high-speed rail environment is suggested. Next, on this basis, a cross-layer optimization model for adaptive cloud collaborative transmission of streaming media, based on DASH protocol, is constructed, and a cross-layer adaptive bitrate selection algorithm for cloud collaborative transmission of streaming media, based on DASH protocol, is proposed to improve the user’s media experience. Finally, the simulation experiment results show that the method proposed in this study can greatly improve the media experience of HSR passengers, and is helpful for the optimization study of the transmission of streaming media in high-speed mobile scenarios.