Abstract: Experiments were conducted to investigate the effects of different nitrate/ammonium ratios and different pH values on the growth of Fusarium oxysporum f. sp. cubense of banana wilt disease. The results show that in the treatments with different nitrate/ammonium ratios, the growth of Fusarium oxysporum f. sp. cubense is strongly restrained at the low pH value (pH=4). At the same pH value, the pathogen growth is significantly inhibited by ammonium as the sole nitrogen source (100% ammonium), and the diameter of the colonies is less than 4 cm. When the ammonium concentration is increased, the pathogen growth is depressed and thoroughly inhibited by ammonium over 5 mmol/L. The penetration through plant cell walls by pathogen is mimicked in this experiment, and it is observed that the pathogen could not penetrate the cellophane membrane when ammonium is the only nitrogen source. In conclusion, the ammonium is convinced to restrain the Fusarium oxysporum f. sp. cubense growth, and its penetration process through the host plant cell wall.