To explore the evolutionary law between single-filament diffraction fringes and double-slit diffraction fringes, a self-made experimental device with dynamically and symmetrically adjustable slit widths was adopted to carry out comparative laser diffraction experiments. (Background) Single-filament and double-slit diffraction have long lacked a unified particle-based theoretical framework to explain fringe evolution[1][2][3][4][5]. (Methods) Self-adjustable double-slit equipment and three sets of comparative optical experiments were designed, together with a complete set of dynamic mathematical derivation based on near-field electromagnetic gradient force. (Results) The experimental results show that double-slit diffraction fringes can be continuously evolved from single-filament diffraction fringes, and both have the structural characteristics of enveloping fine fringes. The particle flow model derived in this paper can uniformly explain the diffraction laws of photons and electrons, which is highly consistent with measured data. (Conclusions) This particle-trajectory interpretation provides a new theoretical perspective for basic optical experiment teaching and diffraction mechanism research. Based on the local near-field interaction characteristics of microscopic particles, a particle flow model with particle trajectory deflection is established. Starting from the action mechanism of near-field electromagnetic gradient force, a complete set of mathematical and physical relational expressions for particle deflection angle, transverse momentum increment and diffraction fringe spacing are derived. Model parameter calibration and self-consistency test are completed by using measured xperimental data. Two groups of differentiated comparative experiments prove that microscopic particles have definite propagation paths when passing through obstacles. The established particle flow model can coherently explain the diffraction imaging laws of photons and electrons uniformly, and is highly consistent with the measured fringe changes. It can provide new reference ideas and theoretical interpretation perspectives for the research on physical mechanism of diffraction and physics experiment teaching.