Abstract: A reversed phase HPLC method was proposed for measuring fungicide MBAMT and its degradation product 2 Amino 5 Mercaptoe 1,3,4 Thidiazole in water. With this experiments were conducted on hydrolysis and photo degradation of the fungicide and a simulated test on degradation of the fungicide in natural ponds. Studies indicated that MBAMT degraded rapidly in water with photo degradation being its leading factor and hydrolysis being a great contributor, and that the degradation product of MBAMT was unstable in water under natural conditions. Hence, it can be concluded that application of the fungicide of normal dosage in paddy fields would not result in hazard to the aquatic environment and fish.