This paper presents an analytic of Obreschkoff approximation for the time-delay network andits relation to the Bessel approximation.An analysis of its approximation characteristic with respect tothe frequency and time domains is carried out.Results show that the Obreschkoff approximation ismore accurate than the Bessel approximation.A practical example is also included. This paper presents an analytic of Obreschkoff approximation for the time-delay network andits relation to the Bessel approximation. An analysis of its approximation characteristic with respect to tothe frequency and time domains is carried out. Results show that the Obreschkoff approximation is more accurate than the Bessel approximation A practical example is also included.