In this paper the authors proposed new design formulae for estimating stresses in buried pipeline with flexible joints by means of the seismic deformation method. The formulae are simpler than that applied in seismic design guidelines for buried pipeline in Japan. Empirical formulae in Guideline of Common Utility Ducts of Japan for estimating pipeline's stress during earthquake agree well with the proposed complete formulae in limited parameter region, but may give quite different results beyond the parameter region. The authors also suggested a calculation procedure to estimate the stress and deformation in buried pipeline caused by settlement due to an earthquake.