Polycrystalline diamond is easy to appear at the edge of single crystal diamond grown by homogeneous epitaxial growth, which makes it difficult to enlarge the two-dimensional surface area of single crystal diamond. In this study, the microwave plasma chemical vapor deposition (MPCVD) is used, the edge of the single crystal diamond (100) crystal face is finely cut and polished to form an inclined surface which is different from the (100) crystal plane at different angles. After being pretreatment, homogeneous epitaxial growth is carried out in a double-substrate waveguide-type MPCVD device with CH₄/H₂ reaction gas. At the same time, the variation of plasma near the inclined plane of (100) crystal edge is analyzed by optical emission spectroscopy to study the effect of the tilting on the growth of the diamond edge. The experimental results show that the angle of the inclined surface of the edge has an effect on the quality of single crystal epitaxial growth of the edge. As the angle of the inclined surface of the single crystal diamond increases, the quantity of edge polycrystalline diamond first decreases and then increases. At an oblique angle of 3.8°, the edge exhibits complete single crystal epitaxial growth characteristics, which conduces to expand the surface area of single crystal diamond. According to the analysis, the inclined surface at different angle changes the surrounding electric field strength and plasma density of the edge, resulting in the change of carbon-containing precursors reaching the surface of the substrate. When the concentration of carbon-containing precursors on the inclined step surface is higher than the growth threshold of layered step, excessive carbon-containing precursors will constantly collide with each other and accumulate to form polycrystalline diamond on the step. When the concentration is lower than the growth threshold of layered step, the carbon-containing precursors on the surface of the substrate will be laid out to form a layered step. Therefore, the edge effect during the growth of single crystal diamond is weakened at the tilt angle of 3.8°, which leads the concentration of carbon-containing precursors on the inclined step surface to be lower than the growth threshold of layered step.