Since Frank proposed "mykorhiza" for the first time in 1885, extensive studies have demonstrated the formation of mycorrhizae between arbuscular mycorrhizal fungi (AMF) and plant roots, and the functioning of mycorrhizae in improving plant gowth and drought adaptability under drought stress particularly in semiarid and arid ecosystems. However, information is limited on the mechanisms how AMF could affect the host plant water uptake, root signal generation and transfer, while most studies have focused on effects of AMF on their physiological and ecological changes in host plants. In this review, progresses in how AMF could balance water relations and affect root to shoot communications are summarized from studies in the last four decades, and possibly related mechanisms are also concluded. These mechanisms include enhanced water uptake, root hydraulic conductance, antioxidant activity, altered hormone relations, osmotic adjustment, aquaporin expression and nutrition absorption. Studies have showed that AMF associated symbioses have usually altered eco-physiological characteristics, e.g. stomatal conductance, plant size and abscisic acid (ABA) content, and thus enhancing the lateral root pressure and vertical transpiration to benefit for host plant's water absorption. The Ohm's law model, which is the most representatively traditional progress in water uptake mechanisms, could further reveal how AMF is able to improve soil water absorption and transport. This mode reveals that mycorrhizal hyphae, which are different from plant root cells, having aseptate or coenocytic and elastic hyphal wall at the tip, and only infrequent, adventitious septa, can contribute to transport water rapidly in host plants under drought stress. Thus, AMF in plant root may be able to feel drier soil more quickly and produce non-hydraulic root-sourced signals earlier. AMF can also affect root to shoot communications, such as inducing signaling cascades for root-sourced signal generation and the improvement of drought tolerance from cellular to whole plant level. Nevertheless, the composition of root exudates are complex, and the mechanisms of root to shoot communications still need to be solved: 1) how AMF help root cells to perceive root water stress; 2) relationships between early drought-gene expression and non-hydraulic root-sourced signal (nHRS); and 3) relationships between late drought-gene expression and hydraulic root-sourced signal (HRS). Possible pathways may further reveal the unknown mechanisms in root to shoot communications that are affected by AMF: 1) the differences in their composition among root exudates and root ingredient under moisture gradients, which may have potential in indicating the perception of water stress signal component; 2) the ABA-binding factor (ABF), which may be as one of the important transcripts to respond to the early drought stress, and Ca²⁺ as a second messenger collaborating ABA to regulates the open and close of guard cells. Therefore, studies on their distribution of ABA and Ca²⁺ in root, stem and leaf under moisture gradients may provide insight into relationships between early drought-gene expression and nHRS; and 3) relationships between the whole plant drought tolerance (e.g. plant type and biomass allocation) and the cell drought tolerance (e.g. antioxidant enzymes and penetration substances), which may address mechanisms involving in the late drought-gene expression and HRS. With the further progresses are made on the contribution of AMF symbiosis to plant water uptake and drought tolerance, we believe that AMF will have potential application in semi-arid and arid agricultural production.