experiment was carried out for two successive seasons (2016 and 2017) at EL- Sharkia governorate. In both seasons tomato; plant "alsa" variety were cultivated to obtain different levels of infestation by Tuta absoluta of tomato crop were sprayed periodically with King chem 5.7% WG (Emamectin benzoate). Results showed simple correlation "r" values obtained were strong significantly negative indicating a strong negative relationship between the density of infestation (Tuta absoluta) and the corresponding crop yield of tomato produced. The simultaneous effect of some tomato pests (Tuta absoluta, Bemisia tabaci and Tetranychus urticae) infestation on the crop yield indicated that the three factors were responsible for 73% and 93% of variability in the average weight of crop yield in 2016 - 2017 respectively. This study aims to the determination of economic infestation threshold level and economic injury level of Tuta absoluta to be used as a tool for controlling Tuta absoluta under Field conditions. Data indicated that (General Equilibrium Position (G.E.P.)) between 55 to 61 larvae / 20 leaves, Economic Threshold Level (E.T.L)] between 57 to 72 larvae / 20 leaves, [Economic Injury Level ( E.I.L)], 78 to 103 larvae / 20 leaves at this level of infestation control measures must be applied.