Zirconium (Zr) has a hexagonal close-packed crystal structure, which exhibits elastic and plastic anisotropy. Internal stresses can be easily generated in the rolling process and the subsequent plastic deformation process. It is critical to evaluate the internal stresses and the deformation mechanisms of Zr alloy materials. The deformation behaviors of Zr alloy influence directly its service life and safety. In this work, compression deformation behaviors of zircaloy-4 (Zr-4) alloy have been studied by the in situ neutron diffraction technique combined with the elastic-plastic self-consistent (EPSC) simulation. A compressive external load is applied along the thickness direction of the rolled plate, which is called through-thickness compression. Electron back-scattered diffraction is used to analyze the texture evolution during the plastic deformation. Transmission electron microscopy (TEM) is used to measure the distribution of the defects in the deformed sample. The EPSC simulation provides the deformation mechanism quantitatively by fitting the in situ neutron diffraction data, and the simulated results is confirmed by the TEM observations. Results show that when the true strain is small (less than 0.55%), prismatic {1010}20> (a> type) slip dominates; however, as the plastic strain is increased, the percentage of pyramidal {1011}23> (c+a> type) slip becomes larger than that of prismatic {1010}20> (a> type) slip, and the pyramidal {1011}20> (a> type) slip and pyramidal {1012}20> (a> type) slip may exist.