Potassium picrate was prepared from picric acid. Potassium hydrate and its crystal structure was determined by a X-ray diffractometer. The results show that the crystal is of orthorhombic system. Space group is Ibca with crystal parameters of a＝0.713 5(1) nm,b＝1.333 2(1) nm,c＝1.912 4(2) nm,V＝1 819.1(3) nm³,Z＝8，D_c＝1.951 g·cm^-3,μ＝13.4 m^-1,F(000)＝1 072.