Abstract: Aiming at the problem of thread galling of the tubing and casing as popularly met in the oil field,a finite element model of the casing round thread is set up,and then used to find out the values and the distribution regularities of the strains on both the inner and outer surfaces of the after-make up coupling.And such data are compared with those as actually measured to verify reliability of the said FE model.Furthermore the FE model is employed to identify to what a extent the connection strength of the coupling is influenced in cases of slight,moderate and serious galling of the thread.As a result the facts as follows are revealed.For slight thread galling,the influence on the coupling connection is so little;for moderate thread galling,if it occurs on the big end of the engaged thread section,the connection strength is reduced by 5%;and in case of serious thread galling,the connection is obviously reduced,and specifically speaking,if such galling occurs on the big end of the engaged thread section,the connection strength is reduced by about 20%,and if it occurs on the small end or in the middle of the engaged thread section,the connection strength is just reduced by 6%~8%.