Objective Ultrasound-based shear wave elasticity imaging has great potential and development prospects in clinical practice. The speed detection for shear wave propagation is the key step in this technique. The accuracy of speed detection for shear wave propagation based on static aperture focused ultrasound emission mode is reduced as the focal length is small. To solve this problem, a detection method based on dynamic aperture control is proposed in this paper. Methods For the different focal length, active array elements were adopted for dynamic control on the size of aperture. The method of “time to peak displacement”, combining with least square algorithm, was used to calculate the propagation speed of shear wave. The method of control variables was adopted for study on acoustic radiation force field, “displacement-time curves” for the marked points and the propagation speed of shear wave in the software platform FieldⅡ. Results Grating lobes were eliminated effectively and ideal “displacement-time curves” with a clear peak were obtained for the marked points with the proposed method. The relative errors reduced compared to traditional method. For example, when the focal length was 7mm, the relative error reduced 16.585%; when the focal length was 9mm, the relative error reduced 15.205%. Conclusions For the small focal length, the proposed method can control the acoustic radiation force properly and increase the accuracy of speed detection for shear wave propagation. The study provides a theoretical basis for the improvement of shear wave-based ultrasound elasticity imaging.