Although the low energy fractional excitations of one-dimensional integrable models are often well-understood, exploring quantum dynamics in these systems remains challenging in the gapless regime, especially at intermediate and high energies. Based on the algebraic Bethe ansatz formalism, we study spin dynamics in the anti-ferromagnetic spin-1/2 XXZ chain with the Ising anisotropy via the form-factor formulae. Various excitations at different energy scales are identified crucial to the dynamic spin structure factors under the guidance of sum rules. At small magnetic polarization, gapless excitations of psinons and antipsinons dominate the low energy spin dynamics. In contrast, spin dynamics at intermediate and high energies is characterized by the two- and three-string states. The dynamic spectra of the identified dominant excitations evolve with clear energy separations when tuning the magnetic field, conveying a simple and straightforward way to clearly identify the novel string excitations in proper condensed matter systems. Our predictions have been experimentally confirmed on the quasi-one-dimensional material SrCo2V2O8, where the details of the experimental observations will also be discussed.