This paper introduces a sine-transform-based \(\tau \) -preconditioner for a specific class of two-level Toeplitz systems and rigorously analyzes its spectral properties. We prove that the eigenvalues of the \(\tau \) -preconditioned matrices are uniformly bounded within the interval [1/4, 9/4], ensuring the linear convergence of the preconditioned conjugate gradient method. This preconditioning strategy is applied to multidimensional nonlocal diffusion models discretized into ill-conditioned multilevel Toeplitz matrices, which belong to the class of matrices under consideration. Numerical experiments demonstrate that, compablue to the conjugate gradient method and multigrid methods, the \(\tau \) -preconditioned conjugate gradient method achieves comparable accuracy and convergence rates while requiring fewer iterations and lower computational costs.