In　this　paper,　a　linear　method　to　determining　intrinsic　parameters　from　two　parallel　line-segments　is　proposed.　Constrains　based　on　the　length　ratio　of　line-segments　are　used　to　solve　the　camera　calibration　problem　from　images　of　two　parallel　line-segments　under　different　conditions.　And　for　each　setting,　we　can　get　linear　solution　for　intrinsic　parameters　of　a　usual　camera.　Simulated　experiments　are　carried　out　to　verify　the　theoretical　correctness　and　numerical　robustness　of　our　results.　©　2013　Springer-Verlag.