In this paper,  the degradation kinetics of diphenyl ketone and malachite green in water has been studied,  including the theoretical analysis of the degradation kinetics of organic compounds in water by using 185nmUV irradiation,  analysis of the reaction rate constant and the effect of temperature,  concentration,  pH and other factors on the reaction rate constant.  A chemical kinetic equation is established and the kinetics rule for degradation of diphenyl ketone and malachite green is discussed.  The degradation reaction is found to be a pseudo-first order reaction.