Lift-off　velocity　of　saltating　sand　particles　in　wind-blown　sand　located　at　1.0　mm　above　the　sand　bed　surface　was　measured　using　a　phase　Doppler　particle　analyzer　in　a　wind　tunnel.　The　results　show　that　the　probability　distribution　of　lift-off　velocity　can　be　expressed　as　a　lognormal　function,　while　that　of　lift-off　angle　follows　an　exponential　function.　The　probability　distribution　of　lift-off　angle　conditioned　for　each　lift-off　velocity　also　follows　an　exponential　function,　with　a　slope　that　becomes　steeper　with　increasing　lift-off　velocity.　This　implies　that　the　probability　distribution　of　lift-off　velocity　is　strongly　dependent　on　the　lift-off　angle.　However,　these　lift-off　parameters　are　generally　treated　as　an　independent　joint　probability　distribution　in　the　literature.　Numerical　simulations　were　carried　out　to　investigate　the　effects　of　conditional　versus　independent　joint　probability　distributions　on　the　vertical　sand　mass　flux　distribution.　The　simulation　results　derived　from　the　conditional　joint　probability　distribution　agree　much　better　with　experimental　data　than　those　from　the　independent　ones.　Thus,　it　is　better　to　describe　the　lift-off　velocity　of　saltating　sand　particles　using　the　conditional　joint　probability　distribution.　These　results　improve　our　understanding　of　saltation　processes　in　wind-blown　sand.