We study the inverse problem with periodic boundary condition for a new class of integrable nonlinear evolution equations. The multiphase periodic solutions for the nonlinear fields (p, q, r) are expressed in terms of the Riemann theta function, which is obtained via the linearization of the flows of the set of auxiliary variables “μj” on a Riemann surface. An explicit case is evaluated to obtain the form of the algebraic curve on which the variables “μj” move.