The invention discloses a space vector modulation scheme of a four-bridge-arm converter based on a gh gamma coordinate system, and belongs to a pulse width vector modulation method of the four-bridge-arm converter. The scheme comprises the steps that 1, three-phase reference voltage va, vb and vc are converted into the gh gamma coordinate system; six intermediate variables x, y, z, s, q and w are calculated according to coordinates of reference voltage vectors in the gh gamma coordinate system; 2, a triangular prism where the reference voltage vectors are located is determined according to the intermediate variables x, q and w; 3, a tetrahedron where the reference voltage vectors are located is determined according to a relation between the reference voltage vectors and five plains in the triangular prism under the gh gamma coordinate system; 4, three variables are selected from the six intermediate variables; action time t1, t2 and t3 of three adjacent basic vectors V1, V2 and V3 are calculated; and 5, a switching device of the converter is switched according to a result, so that output voltage of the four-bridge-arm converter is equivalent to reference voltage. A realization process of an algorithm can be simplified into intermediate variable calculation, intermediate variable judgment and intermediate variable selection; the scheme is clear in thought and simple to realize; and the algorithm is high in calculation accuracy and small in calculation workload.