The photoelastic technique was applied to capture in situ plane stress in a block-on-cylinder contact. This method allows researchers to qualitatively visualize the distribution of principal stress difference during wear processes. Additionally, numerical simulation of the evolution of wear was conducted. The conjugate gradient method together with fast Fourier transform was employed to solve the pressure distribution. Based on the computed pressure, the block wear was solved with Archard's wear law. The subsurface stress was computed using the influence coefficient method. The simulated results of wear and stress were compared with the experimental results; the similarities and differences between the results highlight the usefulness and limitations of the numerical method. However, the photoelastic technique together with the numerical method casts light on the nature of wear.