Abstract: In order to investigate the attenuation law of pesticide concentration in the greenhouse after spraying, studies are made on the pesticide concentrations of the smoking machine within normal temperature after being sprinkled in the greenhouse, and then the improvements are made for the fitness methods of pesticide concentrations presented by D. K. Giles. Comparing with the former method which set the concentration values of the pesticides at the middle of sampling time field to do fitness analysis, the new method is that the concentration values of the pesticides obtained within the sampling stages are correspondent to those of the fitness analyses at three different moments within the sampling stage. At the same time, the engineering criteria is established for the comparison of the curve fitness functions, and it is obtained from this result that in the condition with the sampling stage of 5 min, the sampled data are taken fit for the value of the pesticide concentrations of the second minute within the sampling stages, thus the relative error is minimum between the total amount of the chemicals and the actually-using amount, only with 1.6%. Moreover, it is shown that during the process of pesticide concentration decomposition, any value of the concentrations within the sampling stage is contributed from that of the previous sampling before the sampling stage.