Based on the application of laser active detection using the cat-eye effect, the model errors introduced in existing research due to the neglect of aperture obstruction was addressed. The laser echo efficiency under the influence of the aperture was modeled and simulated under no defocus, positive defocus, and negative defocus conditions. Numerical simulations were performed using Zemax to validate the model and simulation results. The results show that the maximum incident angle of the cat-eye effect decreases with increasing focal length and slightly increases with greater defocus. The echo efficiency decreases linearly with the increasing incident angle, and the rate of decrease accelerates as the focal length increases. When the objective lens radius and reticle diameter are both 25 mm, the focal length is 100 mm, the incident angle is 7.125°, and there is no defocus, the prediction errors in echo efficiency for the existing and proposed models are 152.653% and 1.213%, respectively. The findings enhance the existing theoretical model of laser active detection and provide valuable insights for optimizing detection system performance.