High-aspect-ratio microholes are widely used in aerospace, electronic packaging, biomedical devices, and precision manufacturing. However, their non-contact optical measurement is still challenged by weak bottom signals, false-focus interference caused by stray reflections and scattering inside the hole, and accumulated uncertainty in aspect-ratio evaluation. To address these problems, this paper proposes a multi-feature fusion optical measurement method based on an aspect-ratio constraint for stable measurement of microhole depth and aspect ratio. In this method, a sequence of microscopic images is acquired at different defocus positions through precise axial scanning. Within a predefined region of interest, multiple image features, including sharpness, mean gray level, and contrast, are extracted to establish the response relationship between image characteristics and axial displacement. After min-max normalization, these features are adaptively weighted according to their response dispersion and fused into a comprehensive feature response function. The local extrema of the fused response curve are then extracted as candidate bottom positions. Furthermore, combined with the measured entrance diameter, a reasonable prior interval of the aspect ratio is introduced as a geometric constraint to screen the candidate depths, thereby reducing the uncertainty caused by false-focus points and single-feature judgment. Experiments were carried out on 20 microhole samples with different aspect ratios. The results show that the proposed method can effectively suppress false-focus interference under weak illumination, low contrast, and complex internal reflection conditions. A good linear agreement is obtained between the measured aspect ratios and the standard values, with a fitted slope of 0.997 and an intercept of 0.00912. The mean absolute error, root-mean-square error, and maximum absolute error are 0.0195, 0.0235, and 0.06, respectively. The proposed method provides a feasible and robust approach for non-contact measurement of geometric parameters of high-aspect-ratio microholes and has potential applications in online inspection, quality evaluation, and process optimization in precision manufacturing.