Nitrate-potash salt deposits mainly occur in extremely dry desert regions of the world. In China, the nitrate-potash salt assemblage has been discovered in salt deposits in Turfan and Dawadi of Xinjiang. This paper reports an experimental survey on the physical-chemical relations of the nitrate-potash salt assemblage. On the basis of sufficient experimental data, the equilibrium stability area of humberstonite has been well established and constrained, which has been shown in a set of phase diagrams in the K+ , Na+ , Mg2+/Cl- , NO3- , SO42--H2O system.