Abstract: ‍ ‍Since 6G will be an integrated network with both communication and sensing functions， device-free sensing （DFS） technology that can realize intelligent sensing based on existing communication systems， has become a hot topic in the field of integrated sensing and communication （ISAC） in recent years. Despite significant advancements achieved in DFS technology through persistent research endeavors， persistent difficulties remain， particularly in terms of the low accuracy and poor robustness in real-world environments. Due to the fact that wireless signals are susceptible to environmental factors， the performance is severely dependent on the deployment environment， leading to poor generalizability in new scenarios. Given this context， how to effectively mitigate the impact of scene changes on sensing performance， thus achieving cross-domain based DFS， has garnered widespread attention from both academic and industrial communities. In this paper， the background of the emergence of DFS technology is firstly expounded， and a systematic elaboration of the technical approaches is provided. Subsequently， a demonstration and analysis of the cross-domain issue in DFS was provided， along with the latest developments in current research. Furthermore， the technical challenges faced by this field were discussed. Finally， a prospect of the future research directions of cross-domain based DFS is given.