p-nitrophenol is synthesized using p-nitrochlorobenzene and sodium hydroxide with phase transfer catalyst. Several reaction factors, such as catalyst type, the amounts of catalysts and sodium hydroxide, the concentration of sodium hydroxide solution as well as reaction time, affect greatly the yield of p-nitrophenol. The optimum reaction conditions are as follows: A-1 used as phase transfer catalyst whose consumption is 6% (mole fraction) of p-nitrochlorobenzene; the molar ratio of sodium hydroxide to p-nitrochlorobenzene is 3:1; the concentration of sodium hydroxide solution is 50% (mass fraction). Nitrobenzene, whose molar amount is 2.45 times as much as that of p-nitrochlorobenzene; reaction time is 7 h at 140 ℃ under normal pressure. The final yield of p-nitrophenol is 83.6%.