Mura is a common defect of thin-film transistor liquid crystal display, which seriously affect the quality of the product. Generally, the performances and root causes of Mura are different and require specific analysis. This paper focuses on a fixed position green stripe Mura on a 81.28 cm(32 in) inch product in 8.5 generation line, and studies the defect mechanism through physical analysis, equipment investigation and testing of different producing conditions. The experimental results show that the change of the properties of the G-1 type photoresist used in the green pixel of color filter is the direct cause of the defect. Furthermore, the root cause is confirmed that the zinc phthalocyanine compounds in the G-1 type photoresist have a strong absorption peaks at 600~700 nm of light wave, so it will absorb photons and transform it to free carriers after illumination. The free carriers form additional electric fields, leading to abnormal liquid crystal deflection in this area, showing the macroscopic green Mura. From the two directions of blocking light and reducing the number of photo-generated carriers, two kinds of improved materials are formed by adding high sensitivity light starter and using pigment molecules with higher color concentration. Both material successfully reduce the incidence ratio of the green Mura defect from about 20% to 0, effectively improving the quality of products.