Laser melt injection (LMI) was used to produce WC particulate reinforced metal matrix composites (MMC) layers on Q235 steel. Based on the analysis of the LMI process characteristic and the macrostructure of the MMC layer, the MMC layer was studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that WC particles can be injected into the whole region of the melted pool and distribute uniformly in the MMC layer. New phase of Fe3W3C is observed in the MMC layer due to the injection of WC particles. The microstructure of the MMC layer is quite complicated and can roughly be divided into two regions: the top part and the bottom part. The microstructure in the top part is characterized by many Fe3W3C dendrites surrounded by few interdendrite eutectics. In the bottom, the amount of Fe3W3C dendrites decreases while eutectics increase obviously. The size and morphology of reaction layers around different WC particles inside the MMC layer exhibit obvious difference. Moreover, the particle injection position plays a critical role in the thickness of the reaction layer.