Background It is well known that there is a soil water content threshold (θTHR) for plant growth and physiological processes. It is very import to obtain the θTHR for agriculture water management . However the measurement of θTHR needs specialized and expensive equipment. The θTHR can also be considered as the soil water content of capillary break (θCB). The θTHR can be calculated based on soil water retention curve. But the obtainment of soil water retention curve is time-consuming. Therefore, a simple and rapid prediction of θTHR is the focus of this study. Aims The θTHR can be predicted by estimating the θCB since the θTHR is generally regarded as the θCB. Whether the θCB can be estimated by simple soil parameters such as field capacity (θFC) and soil bulk density (Db)? Is the estimated θCB equal to the measured θTHR? Which of soil or plant is the major factor affecting the θTHR?Methods An formula of B was proposed to estimate θCB. Eight soils from six literature were used to calculate values of θCB. Theses estimated θCB were compared with 16 measured values of θTHR for 12 plant species in the eight soils. The variation in the θTHR and fraction of transpirable soil water (FTSW) with different plant species in the same soil and the same plant species in different soils were analyzed to compare effects of θCB and plant species on θTHR. Results The values of estimated θCB were nearly equal to those of measured θTHR. Highly significant (adjR2=0.9993,p<0.001) linear relationship was found between estimated θCB and measured θTHR with slope of 0.9938 and fixed y intercept of zero. In addition, the values of θTHR for different plant species were close to the same θCB in a soil. The θTHR values for the same plant species were different if θCB were different. Thus, the θTHR varied only with the θCB but not with the plant species. But the threshold FTSW varied due to plant species, not soil. Conclusions The estimated θCB can be considered equal to the measured θTHR. It is the θCB but not the plant that affects majorly the θTHR. Therefore, the θTHR can be predicted simply and quickly based on the estimation of θCB from θFC and Db.