The invention discloses an improved calculation method for a propagation loss prediction model of a shallow sea. The invention puts forward a novel calculation method based on a Marsh-Schulkin shallowsea propagation loss prediction model for near-field abnormal coefficients of seafloors with different slopes, so that sensitivity to seafloor absorption parameters is reduced and the estimation accuracy is improved. Because of influence on the near-field anomaly coefficient calculation by seafloor parameters, a novel extended calculation mode is provided according to differences of upper limit and lower limit accumulation of the near-field abnormality in terms of geometric propagation, so that the influence of calculating the near-field abnormality coefficient is corrected and thus the precision for calculation of any negative gradient, especially for upper and lower wedge landform calculation by an M-S calculation model is improved. The method is simple and is easy to implement and hasthe high applicability.