The invention relates to a formula of imitative wood filling slurry of a building formwork supporting keel and a processing method. The formula comprises reclaimed rubber powder, plant fibers, hydraulic cementing materials, an additive agent and water. The processing method comprises the following steps of: (1) detecting and adjusting the particle size of the reclaimed rubber powder to accord with a combination requirement for later use; (2) carrying out immersion treatment on sawdust or pulverized matters of crop platycodon grandiflorum by using antiseptic oil or coal tar or anthracene oil for later use; (3) firstly, placing the reclaimed rubber powder, the plant fibers and the hydraulic cementing materials processed for later use in a high-speed mixing device according to the proportion of the components, adding water and the additive agent after mixing for 2-3 minutes, mixing for 2-3 minutes again to prepare the imitative wood filling slurry for the building formwork supporting keel. The imitative wood filling slurry has the remarkable advantages of low cost, high strength and convenience for processing.