Abstract: The application of farmland classification results to grain potential productivity depends to a great extent on whether farmland natural quality cent expresses the effect that field quality works on its grain potential productivity correctly. Hereby, considering farmland natural quality cent as field quality limit coefficient(FQLC), the effect of field quality on grain yield was discussed in this study, using a regression analysis method based on the farmland classification results in Tianjin, China. The results showed that the grade index of farmland natural quality was significantly correlated with the standard grain yield, and the influence of farmland quality on grain output was able to be reflected through the farmland classification results. In general, the standard grain yield increased with increasing farmland natural quality cents, which indicated that FQLC could be used to explain the correction of field quality to grain output. However, controllable field experiments are necessary for understanding the mechanism between field quality and grain output, and constructing rational indicator system for farmland quality assessment in further.