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A heavy-rainfall event that occurred in North China during 19–20 July 2016, resulting in severe flooding, was investigated in this study. In this event, high-value total deformation overlapped the precipitation region, implying a close relationship between them. By deriving the non-geostrophic ω equation in a non-uniformly saturated moist atmosphere, the relation between vertical velocity and deformation was diagnosed. The Q-vector divergence on the right-hand side of the new ω equation was divided into three compositions, associated with horizontal divergence, vertical vorticity, and horizontal-wind deformation, respectively. It was found that the deformation component of Q-vector divergence contributed most to the negative Q-vector divergence in the precipitation region, implying an important role of deformation forcing in facilitating the vertical motion. In order to track the precipitation on the basis of deformation, potential deformation was proposed by virtue of the generalized potential temperature. The high-value potential deformation and precipitation were always overlapping, and shared an analogous temporal trend. This means that potential deformation can reflect the variation of heavy precipitation to a certain extent, and can serve as a tracker of the precipitation region.