4-Nitropyrazole(4-NP) was synthesized via a "one-pot two steps" method using pyrazole as raw material in a fuming nitric acid (w=98%)/20% oleum system. The target product was characterized by IR spectrometry, nuclear magnetic resonance spectroscopy, high resolution mass spectrometry and elemental analysis. The single crystal structure was determined by X-ray single-crystal diffractometer The effect of material ratio, reaction temperature, and reaction time on the yield of product was studied. Results show that the best synthesis process is n(fuming nitric acid):n(oleum):n(concentrated sulfuric acid):n(pyrazole)=1.5:3:2.1:1, reaction temperature 50 ℃, reaction time 1.5 h, the highest yield is 85%. The single crystal structure of 4-NP belongs to triclinic crystal system, its space group is P-1 with cell paramaters of a=8.0329(11) Å, b=9.6305(8) Å, c=9.9036(8) Å, α=74.393(7)°, β=81.560(9)°, γ=83.196(9)°, V=727.40(13) ų, Z=6, ρ=1.549 mg·mm^-3, μ=0.132 mm^-1, F(000)=348.