The invention discloses a graded countercurrent heating module combined environment-friendly energy-saving boiler. The boiler comprises a boiler body, a head section, a middle section, a tail section, a collecting section and a discharge opening, wherein the head section is arranged on the upper portion of the boiler body, one or more middle sections are arranged above the head section, the tail section is arranged above the middle section, the collecting section is arranged above the tail section, and the collecting section is provided with the discharge opening. The boiler has the advantages that heat energy can be fully utilized, graded use at different temperatures can be achieved, dry burning accidents can be avoided, emission of particles can be reduced, modular production can be achieved, and the boiler is assembled on site and is convenient to install and transport.