The invention discloses a biomass mechanical engineering material based on fast-growing grass. Raw materials comprise, by mass percentage, 10-20% of a metallic oxide composite additive, 5-10% of puffball powder, and the balance fast-growing grass powder. In addition, the invention discloses a preparation method of the biomass mechanical engineering material based on the fast-growing grass. The value-added exploitation of the fast-growing grass is improved to high additional value from low additional value, and the fast-growing grass is applied to the mechanical engineering material and industrial finished products with long carbon sequestration time, so that maximum and optimal resource utilization of the fast-growing grass and long-term carbon sequestration are achieved, and widening of the application field of the fast-growing grass and building of a high-quality utilization industrial chain about the fast-growing grass become possible.