The invention relates to the field of electronic elements, in particular to a stable cooling device for a power electronic device. The stable cooling device comprises a power tube, wherein a cooling threaded rod is arranged on the power tube; a heat-absorbing nut, a mica spacer, a cooling jacket, a stainless steel gasket and a fastening nut sequentially sleeves the cooling threaded rod from the power tube to the cooling threaded rod; the cooling jacket comprises an upper supporting surface, a lower supporting surface and refrigerating fins; the refrigerating fins are obliquely intersected and fixed between the upper supporting surface and the lower supporting surface; a nylon shaft sleeve is arranged between the cooling jacket and the cooling threaded rod; a laminated steel spring is arranged between the stainless steel gasket and the fastening nut. The stable cooling device disclosed by the invention has the benefits that the power tube is enabled to be closely connected with the cooling jacket; the heat of the power tube is removed by a cooling tube; the stable cooling device is compact and stable in connection and good in cooling effect.