The invention provides a workable flame-retardant styrene butadiene rubber and a preparation method thereof. The workable flame-retardant styrene butadiene rubber is prepared from base rubber and a flame-retardant softening agent through mixing, wherein the flame-retardant softening agent is prepared by adding an olefin metathesis catalyst and a rubber flame retardant into styrene butadiene rubberand carrying out a reaction. Relative to the base rubber and in terms of the addition amount of the softening agent, the workable flame-retardant styrene butadiene rubber is reduced by 0.2 to 2.0 units/part in Mooney viscosity and increased by 0.1 to 1.0%/part in oxygen index.