The invention relates to a preparation method of biological oil modified phenolic resin for foaming, and belongs to the technical field of biomass-based polymer materials. The preparation method comprises the following steps: adding paraformaldehyde, biological oil and basic catalyst which are weighed in proportion into a reaction vessel; reacting to obtain hydroxymethyl biological oil; adding phenol which is weighed in proportion; heating, and adding urea which is weighed in proportion by times; reacting, regulating the pH value of the resin with an acid neutralizer to obtain the biological oil modified phenolic resin. The biological oil modified phenolic resin has the characteristics of high solid content, proper viscosity, high activity, good stability and the like by introducing active components in the biological oil into a product molecular chain to improve the performance of resin, so that the production cost is reduced, and usage of phenol, formaldehyde and other petrochemicalraw materials is reduced, and the environmental advantage is remarkable.