Abstract: The effect of three herbicides on plant physiology is investigated using³²P,¹⁴C isotope methods. The results show that tin early time after herbicides application, all of the three herbicides affect cotton absorbing ³²P. Sethoxydim inhibites³²P, absorption, fluazifop-butyl stumilates ³²P absorptionand quizalofopethyl has almost no effect on³²P absorption. The influence on soybean is less than that on cotton. Three herbicides are all photosynthetic inhibitors,the sequence of their effects is : fluaxifop - hutyl>sethoxydim > quizalofopethyl. One week after herbicides application,the photosynthesis ability of soybean and cotton are gradually restored, sethoxydim and fluazifopbutyl can simulate the³²P absorption ability of cotton and soybean,however ,auizalofop-ethyl has little effect on³²P absorption ability.