thermal stress is an influential factor for the reliability of hpdl and their optical properties. two packages of conduction;cooled;packaged 60w hpdl were selected as the study samples. in order to investigate what reflow factors influence thermo;mechanical of hpld, a cos model is established. in reflow process and working process, hard solder package suffers higher thermal stress. thermal stress mainly comes from reflow process. in reflow process, copper mount will deteriorate thermo;mechanical of hard solder package. there exists shear stress in hpld and it will convert te;polarized power to tm;polarized power. in working process, uniaxial normal stress along the width direction of qw is mainly influenced by coefficient expansion thermal. the displacement of hcs along growth direction is larger than that of cs, whereas the 'smile' value is smaller. 'smile' is mainly impacted by cte of solder and submount. © 2016 ieee.