GNSS/INS ultra-tight integrated navigation system has become a research hotspot in the field of integrated navigation due to its high positioning accuracy, excellent dynamic performance and strong anti-jamming ability. The principle of GNSS/INS ultra-tight integration was introduced, and the advantages and features of ultra-tight integration mode relative to other integration modes were compared based on the analysis of the technical principle. The domestic and international research status was introduced, represented by ultra-tight integration under high dynamics and MIMU/GNSS ultra-tight integration. The key technologies such as fault-tolerant control technology, neural network assistance, and multi-sensor assisted ultra-tight integration were summarized, and the prospect of GNSS/INS ultra-tight integration towards low cost, high precision and strong stability was prospected.