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. The excellent optoelectronic properties of LHP nanocrystals stem from their unique exciton behavior. However, conventional synthesis methods involve rapid reactions, making it challenging to conduct in-situ studies on the exciton dynamics of nanocrystals. To address this challenge, this work developed a novel room-temperature synthesis method that separately controls ionized \mathrmCs^+and coordinated \mathrmPb^2+, successfully achieving the slow growth of \mathrmCsPbBr_3 nanocrystals and laying a foundation for the measurement and research of their in-situ spectra. By establishing an in-situ spectroscopic measurement system, the dynamic evolution of absorption and photoluminescence (PL) spectra during the formation of \mathrmCsPbBr_3 nanocrystals was tracked in real time. The spectra were fitted using the Elliott model, and the temporal evolution laws of key physical parameters such as exciton binding energy ( E_b ) and band gap \left(E_\mathrmg\right) were quantitatively obtained. It was found that during the growth stage of \mathrmCsPbBr_3 nanocrystals (after \sim 4 minutes), E_b and E_\mathrmg exhibit a significant linear correlation, which is in excellent agreement with first-principles calculations. This study not only provides a new method for the dynamic observation of the formation process of LHP nanocrystals but also the revealed intrinsic laws between exciton parameters lay a crucial foundation for understanding their photophysical mechanisms and realizing precise performance regulation.