Aphotochromic triangle terthiophene with phenylethynyl attached was synthesized under Sonogashira coupling condition and fully characterized. The photochromic behavior was investigated in typical solvents. In hexane, the reversibly photochromic process was induced by UV and Visible light. The solution color could be toggled between colorless and pink color. The photo- and thermo-stability were also investigated at 273 and 323 K. It is stable in the dark at the room temperature, while the degradation accelerated with the temperature rising. Correspondingly, the optimized geometry structure and frontier molecular orbitals were calculated. Both the distance between reactive carbon atoms and the HOMO distribution of ring-open form support the photo-cyclization reaction.