The invention relates to a method for preventing false operation of distance III-section protection when a power transmission line is overloaded. The method comprises the following steps: judging whether an action delay of distance III-section protection is reached or not at first, and if not, calculating a power flow transfer characteristic value according to three-phase current, zero-sequence current, positive sequence voltage and an positive sequence impedance angle which are measured at the installation position of distance III-section protection; judging whether the line is short-circuited or overloaded by using a current criterion and a voltage criterion with an identification delay; and if the line is overloaded, blocking distance III-section protection, and, if the line goes wrong, continuously performing distance III-section protection. On the premise of not changing the original delay tripping function of distance III-section protection, when the power transmission line is overloaded, distance III-section protection can be blocked in time no matter the system oscillates or not, and therefore, the cascade trip and accident scope expansion phenomena generated as the overloaded line is cut off through false operation can be avoided.