The invention relates to a fuzzy comprehensive evaluation method for transient power angle instability and voltage instability. The method comprises: (1), establishing a voltage stability and power stability index system; (2), constructing an index s membership function; (3), determining an index weight; (4), determining an integrated fuzzy membership function and obtaining a final fuzzy criterion; and (5), determining a fuzzy determination model of transient power angle instability and voltage instability. On the basis of fundamental principles of power angle stability and voltage stability, related electrical quantity changing rules of a generator, a connecting line, and a load side are taken into consideration comprehensively and fuzzy criteria for evaluating different instability mode instability degrees of the power system are provided, so that technical references are provided for formulating transient stability control measures and arranging operating way of the power system.