A protecting mechanism for a blood sampling device contains: a trigger unit and a switching assembly. The trigger unit includes a lancet holder, a triggering shaft, and a resilient element. The lancet holder has a launching portion, a first outer protrusion, a through orifice, and a first inner shoulder, wherein a bottom end of the triggering shaft moves in the through hole, and the triggering shaft has a first outer shoulder for engaging with the first inner shoulder of lancet holder, the resilient element is fitted with the triggering shaft and abuts against the lancet holder by ways of its bottom end. The switching assembly includes a fixing jacket having an abutting portion, a rotating tube having a first inner protrusion and two opposite second inner protrusions, and a driving sheath having two stopping sets, wherein each stopping set has two second outer protrusions.
