The safety of rockfill dams during initial impoundment has always been an issue of interest for regulatory agencies. Specifically, it is necessary to identify potential tensile strain zones and shear strain concentration zones in which cracks may form. In this paper, a meshless smoothing method is proposed to construct the strain field of a prototype dam based on monitoring displacement data. For verification, this method is applied to calculate the strain field of the Nuozhadu core wall rockfill dam. The results show that the proposed method can provide regulatory agencies with an effective tool for dam inspection during initial impoundment.