Structural and optical properties of InGaN/GaN multiple triangular quantum well (QW) structures with different threading dislocation (TD) densities of 1.5 × 10⁸ (sample A) and 4.5 × 108 cm^-2 (sample B) have been studied. High resolution transmission electron microscopy and x-ray diffraction analysis showed more fluctuation of local In composition in the sample B, which was attributed to the stress field created by the dislocations as it provides a driving force for the migration of In atoms towards dislocations. Severe degradation of photoluminescence intensity of the sample B was also observed at >50 K. The optical and structural properties of the InGaN/GaN triangular QW structures are overall substantially affected by the TD density.