This paper investigates the problem of impact-angle-constrained guidance law design against maneuvering target with large initial heading error. The guidance problem is first formulated in the range domain by leveraging a relative reference frame. Based on optimal control theory and optimal error dynamics, the proposed guidance law is derived analytically without using any linearization assumptions. The approximate closed-form solution and exact numerical solution are presented to analyze the characteristics and physical meaning of the proposed guidance law. The key feature of the proposed guidance law lies in its simple implementation and exact nonlinear nature. Hence, the tolerable initial heading error of the proposed approach is larger than that of conventional linear optimal guidance laws. Numerical simulations are conducted to support the analytical findings.