Abstract: his article sums up the demand of cryogenically cooled dewars for astronomical CCD detector. The general situation of the dewars in China, the characteristics of the TWD type dewar and its test are described. The test results show that Mark Ⅱ and Mark Ⅲ dewars vessel without detector achieve the technical targets as follows:effective volume 2.5L and 1.25L, mass 2.05kg and 3.02kg, preservation time of liquid nitrogen 110h and 116h respectively. Vacuum keeping for more than two years. After connecting with detector, the preservation time of Mark Ⅱ dewars for liquid nitrogen is 40h, the temperature of CCD cold plate achieves-100～-120℃.