In order to study the effect of formic acid/water mixed solvent on the growth morphology of energetic ionic salt dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50), interaction energy between TKX-50 faces and formic acid/water mixed solvent was calculated using molecular dynamics method. The growth morphology of TKX-50 in formic acid/water mixed solvent with different volume ratios (1/4, 1/3, 1/2, 1/1 and 2/1) was predicted by modified attachment energy model, and the effect of temperature on the crystal morphology of TKX-50 was simulated. The results show that changing the volume ratio of formic acid/water in the mixed solvent can significantly change the crystal morphology of TKX-50. When the volume ratio of formic acid/water is 1/2 and the temperature is 298 K, the crystal morphology of TKX-50 is relatively closer to spherical shape. Radial distribution function analysis shows that hydrogen bonds, van der Waals forces and electrostatic forces exist between the (1 1 0) crystal face of TKX-50 and the mixed solvent molecules.