The invention provides a preparation method for starch-based polyether polyol, belonging to the technical fields of chemical novel materials and high-quality utilization of biomass. According to the invention, starch and a mixed solution of polyethylene glycol 200 and glycerin are used as raw materials, and a reaction is carried out under a hydro-thermal condition so as to prepare polyether polyol; and the prepared polyether polyol has a hydroxyl value of 274.89 to 426.36 mg KOH/g, and the liquefaction ratio of starch is as high as 90.4% (wherein when the hydroxyl value is 331.0 mg KOH/g, viscosity is 430.5 mPa.s). The preparation method provided by the invention uses biomass as a reaction raw material, and biomass is safe, environment-friendly and good in biodegradability and avoids usage of catalysts used in traditional preparation methods; equipment used in the method and operation carried out in the method are simple; and the prepared starch-based polyether polyol can be used for preparation of hard polyurethane heat-insulation materials.