The concentration of polymorphs was explored by the ultrasonic measuring technique during crystallization in Solution. The polymorphic form of the crystallized solid, the concentration of the solution, and the transformation of polymorphs were found by the ultrasonic measuring technique. The ultrasonic velocity calibrated at known solid and liquid concentrations has been applied to determine quantitatively the polymorphic compositions for various process conditions. Additionally, it can be used to estimate the solute concentration and the supersaturation of solution during the transformation of polymorphs. Multivariate data analysis from the ultrasonic measuring technique was used to determine the kinetics of polymorph transformation and to simulate the transformation process. It was found that the transformation of polymorphs occurred simultaneously with crystallization of a polymorph in the solution.