Abstract: In the homoepitaxial growth of single crystal diamond by MPCVD, in order to realize the control of the plasma and improve the uniformity of the surface morphology in the two-dimensional expanded growth of single crystal diamond, a circular lining ring with a square hole in the middle, the confinement ring, is placed around the single crystal diamond. The effect of the size of the confinement ring on the uniformity, quality and growth rate of diamond was studied by combining the results of emission spectroscopy, surface morphology, white light interference measurement and Raman spectroscopy. The results showed that under the same conditions of other deposition parameters, increasing the diameter of the confinement ring would reduce the concentration of C2 groups in the plasma, thereby reducing the growth rate of single crystal diamond, but it was beneficial to obtaining high-quality growth surface morphology. When the diameter of the confinement ring increased from 10 mm to 14 mm, the growth rate of single crystal diamond decreased from 10.4 μm/h to 6.4 μm/h, the polycrystalline and dome-shaped defects on the single crystal growth surface were completely suppressed, and the wave packet near 1460 cm-1in the Raman spectrum basically disappeared, and the quality of the single crystal was significantly improved. Two-dimensional expansion growth experiments were performed on the upper and lower sides of the same HPHT seed crystal using confinement rings with a diameter of 14 mm;the dimensions of the two sides were enlarged from 3 mm × 3 mm to 3.82 mm × 3.89 mm and 3.97 mm × 4.07 mm, respectively, and the appropriate confinement ring settings are beneficial to the lateral epitaxy of single crystal diamond.