Electron field emission characteristics of uniformly constructed micro-pyramids of polycrystalline diamond with varying sp(2) content have been systemically investigated. Concurrently, tip surface treatment was performed and emission characteristics of the post-treated tips were evaluated. The experimental results show that the held emission characteristics of the diamond can be enhanced by increasing the sp(2) content and performing surface treatment. The emission current is significantly improved and the turn-on electric held is drastically reduced. Hypotheses are proposed for the effect of sp(2) content and surface treatment on the field emission enhancement of diamond tips : (i) lowering of the work function due to sp(2) defect induced band and impurity desorption, and (ii) increase in field enhancement factor due to sp(2)-diamond-sp(2) microstructures and a field forming process. Analysis of the experimental results indicates that (ii) is the more probable explanation.