The invention discloses an environmentally-friendly size composition for a tyre surface of a tyre and a preparation method thereof. The environmentally-friendly size composition comprises natural rubber, butadiene styrene rubber, butadiene rubber, carbon black, zinc oxide, stearic acid, an antiager, C5 resin, insoluble sulfur, environmentally-friendly arene oil, an accelerator and a homogenizing agent and various other components. The environmentally-friendly size can be prepared by the steps of plastifying and mixing the raw materials and the like. The environmentally-friendly size composition for the tyre surface of a tyre and size obtained by using the preparation method have better breaking strength, tensile strength and hardness, meet environmentally-friendly requirement and are prepared from environmentally-friendly raw materials which do not contain harmful substances, wherein arene oil, C5 resin, insoluble sulfur, carbon black and the like belong to the environmentally-friendly materials; and through adopting the environmentally-friendly raw materials coordinated with reasonable composition design, the environment pollution hidden danger caused in the production and use processes is greatly reduced, and the product has wider safety, economy and adaptability.