The technique to prepare saponin with sea-cucumber treatment waste liquid comprises, filtering the waste liquid to deposite with ethanol, placing, centrifuging; decompressing and condensing the supernatant to remove ethanol; forcing the condensed liquid to flow with velocity 1.5~2.0BV/h through macropore absorption resin; using water to elute and remove the salt, sugar and pigment with same flow velocity; using 60~70% ethanol elution liquid to elute the saponin absorbed on the resin; collecting the elution liquid to condense to extract shape; finally, freeze drying to obtain the product. this invention makes good use of the waste, has no pollutant to environment.