The invention discloses a symmetric fault opening method in an oscillation period by utilizing voltage characteristics. The method comprises the following steps: acquiring a three-phase current and athree-phase voltage at a protection installation position; calculating a positive-sequence voltage amplitude by utilizing the three-phase voltage, and calculating an included angle cosine value of thepositive-sequence voltage and the positive-sequence current according to the included angle of the positive-sequence voltage and the positive-sequence current; when the positive sequence current is less than 0.2 time of the rated current, enabling the cosine value of the included angle between the positive sequence voltage and the positive sequence current to be equal to 1, and calculating the cosine component of the positive sequence voltage; calculating a standard value of the cosine component of the positive sequence voltage by taking the rated voltage of the system as a reference; if thepositive sequence voltage cosine component standard value is greater than or equal to -0.1pu and less than or equal to 0.25pu, calibrating an in-band time scale, and judging that a symmetric fault occurs in the system; judging whether the system enters an acceleration criterion action area or not: if yes, opening distance protection. The method solves the problems that in the prior art, when the system has a symmetric fault, fixed time delay is long, and the fault cannot be rapidly removed.