The surface characteristics of Si3N4 ceramics milled with abrasive waterjet milling technology is studied. The milled surface characteristics and the effect of process parameters on milled surface roughness are analyzed. The results show that the milled surface roughness ranges between 0.55 and 1.1um at the milling conditions under consideration and is changed with the change of process parameters. The milled surface roughness will be significantly decreased at the milling conditions of lower water pressure and larger lateral spacing. The effect of nozzle traverse speed on milled surface roughness is complex, but a traverse speed of 1000mm/min is the optimum speed for AWJ milling Si3N4 ceramics. The milled surface roughness first decreases then increases with an enhancement of standoff distance from 10mm to 30mm, and it also significantly decreases with the increase in abrasive mesh. Therefore, the medium standoff distance of 20mm and finer abrasive are the optimum conditions for AWJ milling Si3N4 ceramics with the process parameters under consideration.