Abstract: OBJECTIVE To obtain the new preparation method of polymorphic form B of pramipexole dihydrochloride and discuss it’s thermodynamics stability and crystal structure. METHODS Polymorphic form B of pramipexole dihydrochloride was characterized by thermal gravimetric analysis(TGA), differential scanning calorimetry(DSC), powder X-ray diffraction(PXRD) and single crystal X-ray diffraction(SXRD). RESULTS Preparation method, crystal structure and polymorphic stability of polymorphic form B of pramipexole dihydrochloride was obtained. The results showed that form B was in the orthorhombic space group P2₁2₁2₁ with formula C₁₀H₁₉C_l2N₃S as the anhydrous form. pramipexole dihydrochloride form B was more stable than pramipexole dihydrochloride monohydrate form in high temperature condition. CONCLUSION Form B of pramipexole dihydrochloride is anhydrous which is more stable at high temperature. Form B has good stability at high temperature.