The invention discloses a technology and device for cooling and purifying high-temperature and high-pressure biomass synthesis gas. The technology comprises the following steps of: (1) subsection cooling, namely cooling the high-temperature and high-pressure biomass synthesis gas coming out of a biomass gasifier to 350-550 DEG C by process water, recovering waste heat to produce medium-pressure steam, and after that, cooling the biomass synthesis gas to 100-300 DEG C, and recovering waste heat to produce low-pressure steam; (2) collecting and removing tar; (3) washing and purifying; and (4) treating the biomass synthesis gas by a wet type electrostatic precipitator, wherein the pressure of the treated biomass synthesis gas is 0.1-1 MPa. The device mainly comprises a tube shell type waste heat boiler, a dry-type gas filter, a vertical smoke tube waste heat boiler, a packless venturi scrubbing tower and the wet type electrostatic precipitator. The technology and the device can be used for controlling appropriate technological parameters by the optimal design of the technical scheme, thus realizing subsection cooling of the biomass synthesis gas, cascade recycling of the waste heat, gradual dust removal and the purification target of tar removal. The technology and the device are simple in equipment, smooth in technology, low in energy consumption, high in efficiency, high in safety and stability and good in economic benefit.