Various types of organic dyes were synthesized to enhance efficiency over past years. Understanding structure-property relationships is a significant issue to develop novel dye for high efficiency dye-sensitized solar cells (DSSCs). In this work, three novel dyes (JY40.1-JY42-1) with ullazine as donor were designed based on the dye sensitizers JY40, JY41 and JY42, and their geometrical structures, absorption spectra as well as optical properties were theoretically investigated by density functional theory (DFT) and time-dependent DFT (TD-DFT). Compared with original dyes, JY40-1-JY42-1 will exhibit better J(sc) due to higher light harvesting efficiency (LHE), regeneration driving force (Delta G(inject)), stronger and broader absorption spectra, superior ICT properties, and lower the driving force of regeneration (Delta G(reg)) as well as reorganization energy (lambda(total)). According to the analysis of interfacial interaction between the dye and electrolyte, JY40-1-JY42-1 have lower electron recombination rate, which further increase V-OC. Hence, ullazine group as electron donor can effectively enhance efficiency of DSSCs according to the above analysis. In addition, JY42 exhibits a better balance in various important properties among three original dyes, which is in good agreement with the experimental results. This work provide a guidance for molecular engineering and screen high-efficiency sensitizers for DSSCs.