Based on the Huygens–Fresnel principle, the intensity distribution expression of double-slit interference with the consideration of slits width is derived. According to the expression, the theoretical results are simulated. It is found that, if the width of the slits cannot be neglected, the interference fringes is not the ideal fringes with same intensity and spacing, but the intensity magnitude decreases with the radial distance increases from center. Moreover, if the distance between two slits is integral multiple of the width of each slit, the fringe may disappear. The explanation of the theoretical results is presented. In addition, the experiment is carried out, and experimental observation is consistent with the theoretical simulation. It is a meaningful discussion for further understanding the teaching and experiment of double-slit interference experiment.