Dynamic　characteristics　of　the　hydraulic　arm　affects　the　mobile　coal　sampling　robot＇s　accuracy　and　efficiency.　The　complex　and　varied　working　conditions　put　many　high　requirements　on　the　stability　of　the　hydraulic　arm.　This　paper　took　the　hydraulic　arm　of　the　MCYY2000　mobile　coal　sampling　robot　as　the　research　object,　and　established　a　simplified　model　of　the　hydraulic　arm　with　SolidWorks.　It　carried　out　the　analysis　under　both　the　condition　of　no-sampling　resistance　and　the　condition　of　variable　sampling　resistance.　The　analysis　was　done　with　the　module　of　multi-body　dynamics　simulation　in　Simulink.　This　paper　helps　to　obtain　the　joint　torques　and　hydraulic　driving　forces　of　the　hydraulic　arm　under　different　conditions.　The　results　provide　a　basis　for　further　work　including　accurate　motion　control,　chatter　reduction　and　safety　improvement　of　the　coal　sampling　robot.