This paper describes the growth condition of PeOOH in the solution of ferrous sulphate with NaOH or NH4OH as precipitant. The crystal forms were observed with electron microscope. The phase composition and phase boundaries were determined by X-ray diffraction. When the precipitant is NH4OH or NaOH, the two phase diagrams of the FeOOH growth in the acid region are similar, but in the alkaline region they are different.