The embedment properties of the dowel-type fasteners is a fundamental parameter that can determine the shear resisting performance of the connections utilized in cross-laminated timber (CLT) structures. To investigate the embedment strength of the smooth dowels inserted in CLT narrow side, totally 504 CLT embedment specimens were tested to evaluate the effects of the influencing factors on the embedment strength, which included the loading angle, the embedment angle, the embedment position, the diameter of the dowels, and the gaps between the lumbers. The existing predictive equations of the embedment strength were validated based on the experimental results, and modified empirical equations were proposed for a more accurate prediction on the average embedment strength. It is found that when the loading direction with a loading angle of 90 degree is parallel to the adhesive layer, for the dowels embedded in the core layer and for those embedded between layers, the average embedment strength decreases by 27.89% and by 33.61% with an increase of the diameter from 8 to 24 mm, respectively. When the loading direction is perpendicular to the adhesive layer, the average embedment strength of the smooth dowels with an embedment angle of 90 degree is 85.25–218.96% higher than that of the dowels with an embedment angle of 0 degree. Furthermore, almost no drop can be identified for the embedment strength of the dowels with an embedment angle of 0 degree when the gap exists in their embedment position. A more accurate prediction on the average embedment strength can be achieved based on the modified empirical equations.