Taking the potential fifth-order MKdV equation as an example to introduce a possible way to construct invariance of a nonlinear PDE. Based on an obtained Bcklund transformation of the potential fifth-order MKdV equation and by solving the corresponding Ricatti form Lax pairs,an invariance of the potential fifth-order MKdV equation is digged out.Thus,just by differential and quadrature procedure,the solutions of the potential fifth-order MKdV equation can be obtained from a known solution.
