The invention relates to a technology and equipment for preparation of synthetic gas by two-stage high temperature biomass gasification. Gasification in the technology is carried out in two stages, namely, primary gasification and high temperature gasification; biomass combustion gas, unreacted solids, tar and the like obtained in the primary gasification are directly delivered into a high temperature vapourizing furnace at high temperature and steam and air are also delivered into the vapourizing furnace so as to carry out high temperature gasification, thereby enhancing thermal efficiency, conversion rate of carbon and cracking rate of tar. In the process of the preparation, heat energy is self supplied, and heat is recovered to improve thermal efficiency; a thermal value of prepared synthetic gas can reach 7 to 8 MJ/m<3>. Equipment for realizing the technology comprises a biomass feed unit, gasification reactors, a dust collector, a heat reclaim unit, a washing unit, an air compressor, etc. The technology and equipment provided in the invention can be used to convert biomass raw materials like agricultural waste into synthetic gas with a high thermal value and low content of tar and are applicable to heat supply by biomass combustion gas, power generation by combustion gas or synthesis of liquid fuels.