The invention discloses a steam generator of a washing machine and a rotary drum washing machine with the steam generator. The steam generator is of a long column drum structure, a water space capable of storing water is arranged at the lower part of the long column drum structure, and a steam space capable of storing steam is arranged at the upper part of the long column drum structure and is communicated with the water space. The steam generator of the long column drum structure is mounted between the side wall of a casing and the side wall of an outer drum of the rotary drum washing machine. The steam generator structure effectively utilizes the space of the rotary drum washing machine, can mount the steam generator under the condition that an original structure of the rotary drum washing machine is not changed so as to add the steam generation function for the rotary drum washing, and has simple structure and low cost.