As a typical phase transition material, vanadium dioxide has attracted much attention in the study of metal-insulator transition behavior since its phase transition temperature is close to room temperature. The experimental results of various modulation provide important clues to studying the vanadium dioxide phase transition mechanism. These experiments not only deepen the understanding of the strong correlation between electrons with different spins in various transition metal oxides, but also make an opportunity for exploring their potential practical applications. Although the phase transition mechanism of vanadium dioxide is still controversial, one has already made tremendous efforts to understand the mechanism of metal-insulation phase transition in the past few decades, which is stimulated from various experiments on vanadium dioxide modulation. Here in this work, the single crystal and polycrystalline vanadium dioxide are investigated. Their modulation mechanisms are studied by using the continuous laser pumping-terahertz probe technique, and it is found that the absorption behaviors of terahertz pulses at the same pump fluence are obviously different. After systematically discussing the representative phase transition mechanism, it is found that the phase transition of single crystal vanadium dioxide is attributed to the Mott-type phase transition dominated by the electronic structure, and that the polycrystalline vanadium dioxide originates from the Peierls-type phase transition occurring during the lattice distortion. In the past, most of the optical modulation was implemented under the condition of femtosecond laser pumping. The new optical modulation method given in this work, is a supplement to previous all-optical modulation experiment and more likely to be conducive to a more in-depth understanding of the modulation mechanism of vanadium dioxides.