In this study, the structural and dielectric behaviors of $Pb_{1-x}Ba_x(Yb_{\frac{1}{2}}Nb_{\frac{1}{2})O_3$ system were investigated as a function of temperature. Although the structure of PYN has not been clearly determined, it is found nevertheless that at transition temperature($\simeq310\circ\C$) high termperature cubic phase undergoes the monoclinic distortion. The X-ray diffraction patterns and DSC curves as a function of temperature reveal that just below the Curie temperature high temperature pseudocubic phase and low temperature monoclinic phase coexist in the narrow temperature range. At room temperature, PYN has a monoclinic lattice with $a\simeqc=8.335$Å, b/a=0.986, and β=89.47°. Extra reflections presumably due to shear atomic displacements are also observed. At the same time, we observe that Ba addition to PYN causes a drop in the Curie point. Meanwhile the maximum dielectric constant becomes greater and its high values are still maintained over a broader range of temperature. The highest dielectric maximum occure at the $Pb_{0.86}Ba_{0.14}(Yb_{\frac{1}{2}}Nb_{\frac{1}{2}})O_3$ composition. When more content doped, the dielectric maximum lowers, but still the temperature range of high-dielectric-constant values are broad. Also, we found that at room temperature $Pb_{1-x}Ba_x(Yb_{\frac{1}{2}}Nb_{\frac{1}{2}})O_3(0.1\le{x}\le0.16)$ exhibits hysteresis on the P-E loop albeit the extra reflections on the X-ray diffraction patterns still remain. Therefore, we refer that in the two-phase coexsitent region one of the two phases is ferroelectrics or ''improper ferroelectrics''. Otherwise, as the content of $Ba(Yb_{\frac{1}{2}}Nb_{\frac{1}{2}})O_3$ increases, the structure of $Pb_{1-x}Ba_x(Yb_{\frac{1}{2}}Nb_{\frac{1}{2}})O_3$ may be changed from the monoclinic to the other structure when 0.1≤x.