Under the action of ultrashort-pulse pump light, the dynamical evolution processes of nonlinear absorption and nonlinear refraction of polycrystalline diamond are studied by using two-photon excitation. In the dynamic experiment of nonlinear absorption, two different recombining processes of activated carriers are observed in the diamond sample, whose time scales are hundreds of picosecond scale and nanosecond scale, respectively, and the time constant of each process under the action of pump light with different energies is obtained accurately. In the dynamic experiment of nonlinear refraction, the positive change of nonlinear refractive index induced by the nondegenerate two-photon absorption process is observed and the third order nonlinear coefficient of the sample is obtained.