Strain-dependent electrical and optical properties of atomically thin transition metal dichalcogenides may be useful in sensing applications. However, the question of how strain relaxes in atomically thin materials remains not well understood. Herein, the strain relaxation of triangular WS2 deposited on polydimethylsiloxane substrate is investigated. The photoluminescence of trions (X-) and excitons (X-0) undergoes linear redshifts of approximate to 20 meV when the substrate tensile strain increases from 0 to 0.16. However, when the substrate strain further increases from 0.16 to 0.32, the redshifts cease due to strain relaxation in WS2. The strain relaxation occurs through formation of wrinkles in the WS2 crystal. The pattern of wrinkles is found to be dependent on the relative angle between an edge of the triangular WS2 crystal and tensile strain direction. Finite element simulations of the strain distribution inside the WS2 crystals explain the experimental observations.