The aim of the study was to establish the influence of the pre-irrigation soil moisture on the photosynthetic potential (FSP) of French beans. The experiment was conducted during the 2010–2012 period in the experimental field of the Agricultural University – Plovdiv. The variants of the experiment were as follows: 1) without irrigation; 2) irrigation at 60% of FC (field capacity); 3) irrigation at 70% of FC; 4) irrigation at 80% of FC; 5) irrigation at 90% of FC. The dynamics of the FSP formation, the values for ten-day periods, for the phenophases and in total for the entire growing seasonwere established. The results showed that during the three experimental years the highest total values of PSP were reportedfor variants 4 and 5, indicating that for the normal development of the beans leaf apparatus, soil moisture should not fall below 80% of FC throughout the growing season. There exists a linear relationship between the seasonal value of FSP and the seasonal evapotranspiration (ET). It is expressed by the following equations: FSP = 374.5 ET – 4680.2 and ET = 0.002 FSP + 69.455. In both cases the equations approximated the experimental points at R2 = 0.804.