Potassium dinitromethane {K[CH(NO₂)₂]}_n was synthesized. The single-crystal structure of {K[CH(NO₂)₂]}_n was determined, which is triclinic, space group P-1 with crystal parameters of a=4.5285(11)Å, b=7.0377(17)Å, c=7.8543(19)Å, α=70.671(3)°, β= 88.557(3)°, γ=75.818(4)°, V=228.58(10)ų, Z=2, D_c =2.094 g·cm^-3, F(000)=144, S=1.060, μ (Mo K_α)=1.077 mm^-1, R₁=0.0457, wR₂=0.1399, (Δp)_max=0.484 e·Å^-3 and (Δp)_min=-1.278 e·Å^-3. Thermal behavior of {K[CH(NO₂)₂]}_n was studied by DSC and TG-DTG methods. DSC result presented two exothermic processes. The self-accelerating decomposition temperature and critical temperature of thermal explosion of {K[CH(NO₂)₂]}_n are 161.0 ℃ and 162.8 ℃, respectively. {K[CH(NO₂)₂]}_n presents lower thermal stability than K(DNDZ) and K(AHDNE), but higher thermal stability than K(NNMPA). {K[CH(NO₂)₂]}_n is relatively insensitive.