Objectives: Anchorage in orthodontics is an important factor.Standard Edgewise technique and Begg lightwire technique use tip-back bend to enhance anchorage,while Straight wire appliance(SWA)technique uses a straight nickel-titanium archwire for teeth aligning and shows early anchorage loss generally.This study aims to explain early anchorage loss of SWA technique through force system analysis of anchorage teeth and to investigate the influence of a-25°tip first molar buccal tube on the force system and early anchorage control.