Northeastern Sichuan is an important district for kalium mine exploration. In this paper, brine reservoir, brine chemical characteristics and underground fluid dynamic field of Jialingjiang and Leikoupo formations of the Triassic were studied. Results suggest that fractured dissolution pore reservoir and dolomite reservoir, with low porosity and low permeability, are the main reservoir for brine of Jialingjiang and Leikoupo formation in northeastern Sichuan. The Xuanhan Dazhou Kaixian Kaijiang area, a salt depression of middle and upper Yangtze region, develops a thick evaporite stratum and is also a leaky fluid area for gas reservoir formation and mine formation. Brine salinity and K+, Br+ abundance are high enough to reach the index standard for industrial exploration. Comprehensive analysis of underground fluid (gas, brine) dynamics in northeastern Sichuan reveals that underground fluid dynamic field was the main mechanism of second K+ enrichment for mine formation. In this mechanism, original sedimentary water sealed in the stratum, which experienced first K+ enrichment through sea water concentration, concentrated again, then migrated to the structure stratigraphy traps, and finally resulted in coupling with gas & mine formation characterized by upper gas and sub brine. Northeastern Sichuan would be an important target area for gas and kalium mine exploration simultaneously.