This　article　proceeds　a　new　method　which　can　continuously　prepare　emulsion　by　using　a　venturi　tube,　to　achieve　the　goal　of　emulsify　diesel　oil,　methane　and　water.　The　diesel　oil　comes　in　at　the　entrance　of　the　venturi　tube.　The　solution　of　methane　and　water　comes　in　at　the　throat　of　venturi　tube　and　mixes　with　diesel　oil　to　form　emulsion.　The　preparation　system　is　designed　and　the　structure　parameter　of　the　venturi　tube　is　calculated.　Then　FLUENT　is　used　to　do　a　series　of　numerical　simulation　of　the　flow　in　the　venturi　tube　under　different　parameters　of　spread　angle　and　ratio　of　length　to　diameter,　thus　deciding　the　best　parameters　which　are　8　degree　and　1.25.　The　basic　data　for　the　design　of　experimental　system　is　provided.