The invention discloses a cylindrical low-nitrogen energy-saving pressure-bearing water pipe boiler which comprises an upper seal head, a shell, a burner distribution head, a water-cooled wall tube bundle, a water-cooled flame tube bundle, a radiation tube bundle, a high-temperature convection tube bundle, a low-temperature convection tube bundle, a descending tube bundle, a lower seal head, an external condenser, a pre-mixer and a matched fan, a water supply pump, a gas valve group, a controller and the like. A burner achieves side face gas feeding, and densely-arranged pipes, a metal pore plate, a ceramic pore plate and the like are adopted for preventing fire return and stabilizing flame. The burner is detachable, thereby facilitating maintenance and repair. The water-cooled flame tubebundle of the burner distribution head is arranged in a plane or convex shape, so that the space of a hearth is utilized to be maximum; and the water-cooled flame tube bundle on a boiler body is adopted to cool the flame, so that the heat distribution problem of the water-cooled burner is solved. Machine-boiler integration of plane and curved surface burners is achieved, the structure is compact,low-nitrogen and ultra-low-nitrogen combustion are achieved at lower excess air coefficients, and the technical monopoly of foreign low-nitrogen burner manufacturers in the field of steam boilers is broken through.