The utility model discloses a biomass steam generator, including lower part base, upper portion body, fire observation hole, flame retardant coating, heat preservation, cubic tuber pipe, smoke box, soot blower, inspection hole, the inside intercommunication of lower part base and upper portion body constitutes furnace, form 3 at least transportation work style ways in the steam generator, access to lower part, the upper portion of lower part base, the furnace upper portion of lower part base respectively. The lower part base even has inlet pipe, air -supply line, the lower part base is equipped with the grate, the 3 at least transportation work styles that form in the steam generator are said including wind channel, secondary air duct, cubic wind channel, the grate bottom is connected to the one end in a wind channel, and grate upper portion is connected to the one end of secondary air duct, furnace upper portion is connected to the one end in cubic wind channel. The utility model provides a biomass steam generator has that safety, high efficiency, energy -conservation, environmental protection, overall structure are compact, area is little, the installation is swift, degree of automation is high, an easy operation, running cost low grade advantage.