The invention discloses a preparation method of a green and environmental protection tanning agent, comprising the following steps: weighing starch, deionized water, sodium hydrogen sulfite, CMC, SDS, silicone oil, op-10, sulfur alcohol and NaOH solution, adding the starch, the deionized water A, sodium hydrogen sulfite, CMC, SDS, the silicone oil, op-10, sulfur alcohol and the NaOH solution to a flask, heating to 50-60 DEG C while stirring, then adding hydrogen peroxide A, heating to 94-98 DEG C after constant temperature stirring for reaction, then cooling to 75-85 DEG C, adding HCL and then dropwise adding an initiator and a monomer, and cooling to room temperature after constant temperature stirring for reaction, thus obtaining the green and environmental protection tanning agent. The green and environmental protection tanning agent prepared according to the method disclosed by the invention can effectively improve the water resistance and shrinking temperature of leather, and de-tanning is not easy to cause.