This study focused on the investigation of the edge effect of diamond films deposited by microwave plasma chemical vapor deposition. Substrate bulge height $ \Delta h $ is a factor that affects the edge effect, and it was used to simulate plasma and guide the diamond-film deposition experiments. Finite-element software COMSOL Multiphysics was used to construct a multiphysics (electromagnetic, plasma, and fluid heat transfer fields) coupling model based on electron collision reaction. Raman spectroscopy and scanning electron microscopy were performed to characterize the experimental growth and validate the model. The simulation results reflected the experimental trends observed. Plasma discharge at the edge of the substrate accelerated due to the increase in $ \Delta h $ ($ \Delta h $ = 0–3 mm), and the values of electron density ($ {n}_{\mathrm{e}} $), molar concentration of H ($ {C}_{\mathrm{H}} $), and molar concentration of CH₃ ($ {C}_{{\mathrm{C}\mathrm{H}}_{3}} $) doubled at the edge (for the special concave sample with $ \Delta h $ = −1 mm, the active chemical groups exhibited a decreased molar concentration at the edge of the substrate). At $ \Delta h $ = 0–3 mm, a high diamond growth rate and a large diamond grain size were observed at the edge of the substrate, and their values increased with $ \Delta h $. The uniformity of film thickness decreased with $ \Delta h $. The Raman spectra of all samples revealed the first-order characteristic peak of diamond near 1332 cm⁻¹. When $ \Delta h $ = −1 mm, tensile stress occurred in all regions of the film. When $ \Delta h $ = 1–3 mm, all areas in the film exhibited compressive stress.