In this work, 4H-SiC epilayers were performed on 4 degrees off-axis Si-face substrates by horizontal hot wall chemical vapor deposition (HWCVD). A new type nominal "washboard-like" triangular defects without particulate located at their apex were observed. The microstructure and formation mechanism were investigated by micro-Raman spectroscopy, electron backscatter diffraction (EBSD) and cross-section transmission electron microscopy (TEM). Characterization results indicate that the triangular defects observed have a 3C-SiC nature. In addition, the phenomenon that a serious of other triangular defects of which the vertices arranged in a row neatly with the new type nominal "washboard-like" triangular defect was observed. Based on these observations and analysis, a model of the formation mechanism of the triangular defect had been proposed. In this model, the 3C-SiC crystal formed by 2D nucleation of adatoms on the terraces is mainly triggered by the scratch in the substrate.