The invention discloses a preparation method for ecotypic bentonite modification detergent, which comprises the following steps of: adding calcium bentonite into sulfuric acid solution; carrying out heating reaction for 5-10 hours; standing, filtering, and drying; grinding to obtain an active bentonite product; heating a certain quantity of water and active bentonite to 70-90DEG C to obtain liquid b; adding modifying agent cocamidopropyl into the liquid b, and reacting at 70-90DEG C for 7-12 hours to obtain solution c containing cocamidopropyl modified bentonite; successively adding fatty alcohol-polyoxyethylene ether-9 and PEG(polyethylene glycol)-80 into the solution c for stirring and dissolving; adding cocamidopropyl betaine, sodium laureth sulfate-9 and water; and stirring at 40-80DEG C for 0.5-2 hours. The bentonite modification detergent prepared with the preparation method disclosed by the invention has a strong cleaning stain resistance capability, has the advantages of even and vivid color, good biodegradability and low cost and is an environmentally-friendly ecotypic detergent, and the COD (chemical oxygen demand) value of detergent washing raffinate is very small.