Maths model based on wo-dimensionalhas was built to simulate the velocity and pressure field of the growth of diamond film. Firtstly，the plasma jet flow is supposed as steady state incompressible gas, which meets with Reynolds-averaged Navier–Stokes equations. The model of the growth of convex diamond film considers different convex height of Mo substrate. The velocity and pressure field were simulated by CFD respectively.The simulational results show that, the distributions of velocity and pressure fields were fluctuant in reaction chamber. When convex height of Mo substrate was 9mm, DC plasma jet was smoother than the other heights, thus, we predicts that diamond film easily grows. Meanwhile, we prepared four diamond films in different heights of substrate, by DCPJCVD. Raman spectra were used to investigate the quality of convex diamond film. It was found that, when the height of convex substrate was 9mm, convex diamond film had only diamond characteristic peak. It is obvious that numerical analysis help us predict the distributions of velocity and pressure fields and synthesize high quality convex diamond film.