Ghost imaging and diffraction, inspired by the Hanbury Brown and Twiss effect, have potential in both classical and quantum optics regimes on account of their nonlocal characteristics and subwavelength resolution capability, and therefore have aroused particular interest. By extending the correspondence imaging scheme, we utilize the positive and negative intensity correlations in diffraction and perform subwavelength diffraction with pseudo-thermal light. In the experiment, a subwavelength (λ/2) resolution and a better signal-to-noise ratio (10.3% improvement) are simultaneously achieved. The scheme can be utilized as a complement to the existing ghost imaging scheme to improve image quality.