In recent years, lead halide perovskite (LHP) nanocrystals have attracted considerable attention due to their excellent optical properties, including high photoluminescence quantum yield (PLQY), tunable band gap, narrow emission peak, large absorption cross-section, and long exciton coherence time. These outstanding optoelectronic characteristics arise from their unique exciton behavior. However, conventional synthesis methods involve rapid reactions, which hinder in-situ investigations of nanocrystal exciton dynamics. To overcome this limitation, this work develops a novel room-temperature synthesis approach that independently controls ionized Cs⁺ and coordinated Pb²⁺, thereby enabling the slow growth of CsPbBr₃ nanocrystals and establishing a foundation for in-situ spectral measurement and analysis. By implementing an in-situ spectroscopic measurement system, the real-time dynamic evolution of absorption and photoluminescence (PL) spectra during CsPbBr₃ nanocrystal formation is successfully tracked. The spectra are fitted using the Elliott model, allowing quantitative determination of the temporal evolution of key physical parameters, such as exciton binding energy ( E_\textb ) and band gap ( E_1 ). It is observed that during the growth stage of CsPbBr₃ nanocrystals (after ~4 min), E_\textg and exhibit a strong linear correlation, in excellent agreement with first-principles calculations. This study not only introduces a new methodology for dynamically observing the formation process of LHP nanocrystals but also reveals intrinsic relationships among exciton parameters, thereby providing a crucial foundation for understanding their photophysical mechanisms and enabling precise performance regulation.