The Jiangmen Underground Neutrino Observatory (JUNO) is a multi-purpose neutrino experiment under civil construction. The central detector consists of 20 kton liquid scintillator (LS) surrounded by around 18000 20-inch photomultipliers (PMTs) and 25600 3-inch PMTs. The primary physics goal of JUNO is neutrino mass ordering determination by precisely measuring the fine oscillation patterns of reactor neutrinos with a 53 km baseline. Antineutrinos are detected through the inverse beta decay channel $\bar\nu_e+p→e^++n$ in the LS, where the positron carries most of the neutrino energy. To reconstruct a precise positron energy spectrum, the mapping between numbers of photoelectrons on PMTs and the true positron kinetic energy is crucial, and depends on the positron energy nonlinearity and resolution response in the LS. Considering that the common calibration sources are almost all $\gamma$ sources, the construction of a calibration-based model to connect energy response of $e^\pm$ with that of $\gamma$ is strongly motivated. Once done that, the positron energy response can be calibrated with the existing sources. In this poster, a unified model for both nonlinearity and resolution in LS detectors is presented. The energy resolution contributions by scintillation light and Cherenkov light have been studied in details. Also the utilization of high energy samples, Michel electrons, has been discussed as a potential method to provide more constraints to the model fitting up to 60 MeV.