We theoretically construct a rectangular phononic crystal (PC) structure surrounded by water with C2v symmetry,and then place a steel rectangular scatterer at each quarter position inside each cell.The final complex crystal has two forms:the vertical type,in which the distance s between the center of the scatterer and its right-angle point is greater than 0.5a,and the transverse type,in which s is smaller than 0.5a (where a is the crystal constant in the x direction).Each rectangular scatterer has three variables:length L,width D,and rotation angle θ around its centroid.We find that,when L and D change and θ is kept at zero,there is always a linear quadruply degenerate state at the comer of the irreducible Brillouin zone.Then,we vary θ and find that the quadruply degenerate point splits into two doubly-degenerate states with odd and even parities.At the same time,the band structure reverses and undergoes a phase change from topologically non-trivial to topologically trivial.Then we construct an acoustic system consisting of a trivial and a non-trivial PC with equal numbers of layers,and calculate the projected band structure.A helical one-way transmission edge state is found in the frequency range of the body band gap.Then,we use the finite-element software Comsol to simulate the unidirectional transmission of this edge state and the backscattering suppression of right-angle,disorder,and cavity defects.This acoustic wave system with rectangular phononic crystal form broadens the scope of acoustic wave topology and provides a platform for easy acoustic operation.