The invention discloses a preparation method of a green early-strength type concrete water reducing agent, and belongs to the technical field of concrete additives. Weathered coal is pulverized through wet method ball milling and then is mixed with methane liquid for fermentation, after reaction with a sodium hydroxide solution, a filtrate is condensed and a concentrated solution is prepared, then cockspur grass roots and pumpkin are pulverized and are then subjected to mildewing degradation, after centrifugal separation, a supernatant is collected, finally the concentrated solution and the supernatant are blended with sodium silicate and a silane coupling agent, and through spray drying, the green early-strength type concrete water reducing agent is obtained. The weathered coal and effective components in degradation products of cockspur grass and the pumpkin, under the action of the silane coupling agent, can generate stronger absorption function with concrete particles, the electronegativity of the concrete particles is improved, and the concrete particles and sodium ions in the green early-strength type concrete water reducing agent form a diffused electric double layer, so that the colloidal stability is improved effectively, the early strength is improved, the concrete viscosity is reduced, the concrete mobility is improved, and the problem that the early strength is poor after the traditional concrete water reducing agent is used is solved effectively.