Abstract: In the direct coupled Microwave Plasma Chemical Vapor Deposition （MPCVD）diamond film device, magnetic mirror is used upon quartz tube reaction chamber lens to better constraint shape of plasma ball. So plasma ball become to "dish plate". The density of plasma ball is improved. The basic parameters: 2.5 kPa,450 ℃,Ar 40 sccm,CH₄ 4 sccm, H₂ 60 sccm, which is constant, the diameter sedimentary area of growth from 30 mm to 50 mm, deposition rate increased from 3.3 μm/h to 3.8 μm/h,the maximum reflected electric current reduced from 15 μA to 5 μA.Thus, deposition of the wall of quartz and the watching window is reduced greatly.And, the microwave energy is used effectively to made high quality diamond films or diamond like carbon films.