Context. The Period-Luminosity relation for δ Scuti stars is crucial for galactic distances measurement. Estimating metallicity of δ Scuti is thus important for calibrating this relation and ensuring its accuracy. Aims. The aim of this study is to establish relations between the Fourier parameter of light curves and metallicities to estimate the metallicities of δ Scuti. Methods. I first classify δ Scuti stars into six types based on the morphology of their light curves. I then establish the relations between the Fourier parameters and metallicity for each of the six types. Results. For high-amplitude δ Scuti stars (HADS), the metallicity is lower when a light curve shape approaches the rapid-rise and slow-decline form (Type I). While for low-amplitude δ Scuti stars (LADS), the results show the opposite correlation. For Type I HADS and Type III (slow-rise and rapid-decline forms) LADS, the 𝐴1-P relations provide the best metallicity fitting results. In comparison, the best relation for symmetric forms (Type II) HADS is constructed based on 𝐴2-𝑃. Overall, for Type I and Type II LADS as well as Type III HADS, relations based on period (𝑃) show the highest accuracy. Conclusions. My study indicates that the period (𝑃) is an essential parameter for estimating metallicity. For types with lower metallicity, incorporating the amplitude (𝐴) parameter into the relation leads to a more accurate estimation. In the future, this relation-construction approach could be further utilized in studies of metallicity estimation for other types of pulsating variable stars.