The invention provides a small-sized biomass chopped-material direct-fired water boiler. The water boiler comprises an automatic feeding mechanism and a boiler body, wherein the automatic feeding mechanism consists of a loading box, a feed box, two horizontally placed ejecting rollers and a spiral auger, a draw plate is arranged at the bottom of the loading box, the feed box is positioned below the loading box, the ejecting rollers are mounted in the feed box and provided with radiant pick teeth, and the spiral auger of which the output end is communicated with a feed inlet of the boiler body through a feeding pipe is positioned below the ejecting rollers; and the boiler body consists of a dust collection room, a primary air inlet pipe, a primary air room positioned above the dust collection room and communicated with the primary air inlet pipe, a secondary air inlet pipe, a flue gas steering plate, a secondary air distribution pipe positioned above the primary air room and communicated with the secondary air inlet pipe, a smoke exhaust pipe arranged at the top of a hearth, a flue gas entrained flow air inlet pipe positioned on the side wall of the smoke exhaust pipe and a water jacket on the outer wall of the hearth. The small-sized biomass chopped-material direct-fired water boiler has the advantages of simple structure, low fuel and running costs, cleanliness and convenience in use and high heat efficiency, and is suitable for heating, bathing and the like in wide rural-urban fringe zones and small towns.