Abstract: Analytic formulas on acoustic interference patterns are derived by ray method to guide acoustic measurements in shallow water,especially those with horizontal distances less than ten times of water depth.We take some reasonable and necessary approximations and neglect those less important rays for a more concise expression.Monofrequent signals,complicated signals and frequency-modulated signals are all studied.The analytic formulas represent the quantitative relationships between the interference-pattern and the signal frequency,bandwidth,depth of source and horizontal distance.Several inferences are also deduced from the formulas.Both numerical simulations and experiment data are presented to prove that these formulas and their inferences can describe the critical characters of the acoustic interference pattern in waveguide with satisfying precision.