Abstract:Tetranychus urticae is one of the most important pests in fruit production. For the sake of economically and effective control the damage, the investigation was carry out to find its population dynamics and apple‘s yield loss, the concerns model was established hereby. And then, the economic injury level (EIL) based on T.urticae in apple orchards was studied. The results show that there were significant correlation between the mite days (MDs) and apple yield losses (Q=0.0157+0.00016MD, R2=0.9567).When the economic tolerable injury level is 4.57%, if the mite‘s population density of per leaf as evaluation methodology, the EIL should be ≤7.70 per leaf before early July 3th, and ≤8.70 per leaf before July 25. When the accumulative MDs as evaluation methodology, the EIL should be ≤29.93 before early July 5th and EIL≤122.95 before July 25. The total MDs should≤188.70 in the whole growing season.