The lifetime of roll-bits with inserted tooth will be obviously decreased while drilling in strata and the tungsten carbide can be integrally separated from the roll-cone，which will need more trip out time to replace the roller bit． This study provides an entire analysis on stress as well as strength for teeth and tooth holes in loaded conditions． Qualities of tooth drop from matrix within roller bit． The optimized interferences of teeth inserted into the bit can be reasonably obtained by the critical interference derived from some relevant influence factors on the tooth-fixing quality of roller bits．