The　evaluation　of　the　drag　force　on　non-spherical　particles　is　of　great　importance　in　a　wide　range　of　areas.　In　the　present　paper,　a　general　analytical　expression　for　the　drag　force　on　non-spherical　particles　in　the　free　molecular　regime　is　obtained　based　on　the　gas　kinetic　theory.　The　obtained　expression　is　applicable　to　rigid　convex　non-spherical　particles　suspending　in　a　diluted　gas,　wherein　multiple　collisions　between　the　gas　molecules　and　the　particle　are　ignored.　Based　on　the　Maxwellian　scattering　model,　i.e.,　specular　and　diffusion　collisions　between　gas　molecule　and　the　particle,　the　general　analytical　expression　for　the　drag　force　on　particles　can　be　derived　by　evaluate　the　momentum　transfer　between　the　gas　molecules　and　the　particle　upon　gas-particle　collisions.　As　examples,　the　expressions　for　drag　force　on　several　common　non-spherical　particles,　such　as　spheres,　cylinders,　ellipsoids　and　cones,　are　also　presented,　which　are　consistent　with　the　results　in　open　literatures.　It　is　found　that　the　drag　force　on　non-spherical　particles　depends　on　the　geometric　shape　and　orientation.　However,　the　specific　expressions　for　drag　force　on　non-spherical　particles　are　mathematically　too　complex　to　be　employed　in　practical　application.　Considering　that　the　particle　is　expected　to　undergo　a　rapidly　rotation　in　the　case　of　weak　potential　field　in　the　free　molecular　regime,　so　the　distribution　of　the　particle　orientation　should　be　a　uniformly　random　distribution.　Then,　the　expression　of　the　orientation-averaged　drag　force　on　non-spherical　particles　can　be　derived　by　introducing　the　random　orientation　distribution　of　the　particle.　It　is　found　that　the　orientation-averaged　drag　force　is　proportional　to　the　surface　area　of　the　non-spherical　particle,　and　the　corresponding　coefficient　is　independent　of　the　particle　size　or　shape.　The　findings　in　the　present　paper　can　be　employed　to　simplify　the　calculation　of　the　drag　forces　on　non-spherical　particles　in　the　free　molecular　regime.　©　2024　Chinese　Society　of　Theoretical　and　Applied　Mechanics.　All　rights　reserved.