The invention discloses a method for preparing cyanoacetic acid through continuous dehydration. After chloroacetic acid is neutralized, cyanided and acidized to obtain cyanoacetic acid water solution, multi-effect evaporation and forced circulation evaporation are adopted and coupled for continuous dehydration, in addition, continuously separated sodium chloride is removed in the dehydration process for preparing the cyanoacetic acid, when the multi-effect evaporation is used for preparing the cyanoacetic acid, the steam consumption is reduced, and in addition, the sodium chloride is filtered during the proceeding of each effect, so the separated sodium chloride can be filtered and removed in time, the solid-liquid ratio is reduced, filter equipment can be more favorably selected, the operation is simple, the equipment utilization rate is high, the steam consumption is low, in addition, the dehydration time is short, and the cyanoacetic acid yield is high.