Despite the Czochralski technology having been commonly used for manufacturing bulk single crystals, crystal quality and production are still limited by the insufficient understanding of the crystal-melt interface. Herein, we propose a novel perspective on the voltammetric characteristics of an equivalent circuit model to reveal a growing boule. Specifically, by elucidating the interface electromotive force during lithium niobate crystal growth, we find the nonlinear conduction behavior at the crystal-melt interface, representing the characteristic of a PN junction. Further regarding this interface as a rectifier diode with parasitic resistance, the voltampere curves will draw abundant crystal growth information in situ. For example, the real-time cyclic voltammetry curves are highly consistent with the circuit simulations, whose series resistance well predicts the actual length of the as-grown crystal. More importantly, this equivalent circuit model establishes a simple but effective perspective for revealing the nature of the growth system, encompassing the kinetics of high-temperature phase transition and the thermodynamics of quantitative composition control.