Laser melt injection (LMI) was used to prepare single crystal particle reinforced WCp/Ti-6Al-4V functionally graded materials (FGMs) layer on Ti-6Al-4V. In situ tensile test in scanning electron microscope (SEM) was employed to study the crack formation and propagation of the FGMs layer. The micro fracture behavior was also studied. The results show that there are mainly two failure mechanisms: WC particle cracking and WCp/Ti interface decohesion. WC particle cracking forms the majority of the crack nucleation. In contrast, WCp/Ti interface decohesion is a rarely observed phenomenon, which usually occurs at higher strains. In addition, the regular cellular reaction layer formed in LMI plays a positive role in the load transfer from the matrix to the particle. During the tensile test, the stress state of WCp gradually changes from initial compressive stress to tensile stress. Furthermore, the maximum tensile stress inside the WC particle is about 2000 MPa, which is much higher than the critical fracture strength of single crystal WCp