Thermal　depolarization　caused　by　birefringence　is　a　major　factor　that　limits　the　output　power　of　linearly　polarized　Nd:YAG　laser.　Compared　with　conventional　[111]-　cut　Nd:YAG　rod,　the　thermal　depolarization　depends　on　the　polarization　direction　for　the　[100]-　cut　Nd:YAG　rod.　The　linearly　polarized　output　power　can　be　improved　by　suitable　modification　of　the　polarization　direction　of　oscillate　laser.　The　[111]-　and　[100]-　cut　Nd:YAG　rods　are　used　as　the　gain　medium　and　the　Cr4+:YAG　crystal　is　used　as　the　saturable　absorber　for　passively　Q-switched　laser.　The　experiment　demonstrates　that　in　comparison　with　conventional　[111]-　cut　Nd:YAG　rod,　highly　stabled　output　with　high　extinction　is　achieved　by　using　the　[100]-　cut　Nd:YAG　rod　as　the　laser　crystal.　The　extinction　ratio　is　500:1　and　polarized　output　stability　is　higher　than　96.5%.