The effects of stress, electron beam irradiation and second phase particles on zirconium hydride precipitation and growth in Zircaloy-4 were investigated using in-situ transmission electron microscope observation. Results show that with the tensile stress the cracks are likely to propagate along hydrides and new hydrides are formed at the crack tip along the vertical direction of the applied stress. A process of precipitation, cracking, re-precipitation and so on, induced by tensile stress, causes delayed hydride cracking (DHC). Under the high irradiation of converged electron beam, the hydrides decompose in the Zircaloy-4, and new hydrides prefer to precipitate around the unoxidized Zr(Fe, Cr)2 particles, and the re-precipitated hydrides are fcc-structure δ phase.