The invention discloses an automatic drying method of a roller washing machine. The method comprises the following steps: presetting various parameters; calculating original weight mA of the clothes by a controller before washing; entering a drying mode I for drying after washing and dewatering; selecting a drying mode II or the drying mode III according to the condition; controlling a heating tube to close by the controller when meeting the drying ending condition so as to end drying; and cooling the clothes. Compared with the prior art, the automatic drying method has the advantages that the high-power drying mode I is selected; and the low-power drying mode II or drying mode III with lower power is selected according to the temperature and humidity and the clothes weight change, so that the time required for drying the clothes is greatly shortened; the problem of insufficient clothes drying or excessive clothes drying is avoided; and the drying quality of the clothes is ensured.