The invention discloses an environment-friendly synthetic low-coke-yield fire-resistant L-QB300 organic heat carrier composition. A compound of 50% (m) of poly-alpha-olefin and 50% (m) of triaryl phosphate is used as basic oil and is matched with various compound additives. The environment-friendly synthetic low-coke-yield fire-resistant L-QB300 organic heat carrier composition comprises an antioxidation additive, a high-temperature antioxidant, an antioxidant, a metal passivator, a metal deactivator, an anti-coking agent, an anti-rust agent, an alkali number retention agent, an anti-foaming agent, a reinforcing agent and a synergist. The environment-friendly synthetic low-coke-yield fire-resistant L-QB300 organic heat carrier composition has the advantages of high thermal stability, use temperature range of minus 60 to 400 DEG C of series of products, long service life, reproducibility and biodegradability.