The influence of an axial high magnetic field (up to 12 T) on Sn dendrite morphology in directionally solidified Pb-Sn alloys has been investigated experimentally. Results show that the magnetic field has modified the Sn-dendrite morphology dramatically. Indeed, it has been found that the applied magnetic field has destroyed the Sn-dendrite array and caused the occurrence of the columnar-to-equiaxed transition (CET) at lower growth speeds (R < 20 mu m/s). Along with the occurrence of the CET, equiaxed grains are aligned under the magnetic field. The effect of the magnetic field weakens as the growth speed increases. Further, the amplitude and distribution of the thermoelectric magnetic force (TEMF) and thermoelectric magnetic convection (TEMC) during directional solidification of Pb-Sn alloys have been studied. Numerical results reveal that the TEMF acts on the tip and bottom of the dendrite/cell. The value of the TEMF increases with the magnetic field and the maximal value of the force is of the order of 105 N/m(3) under a 10 T magnetic field. The above results should be attributed to the coupling effects between the TEMF and the magnetization force. Present work may initiate a new method to prepare the "aligned equiaxed grains" via an applied high magnetic field (B >= 8T) at a low growth speed (R <= 20 mu m/s) during directional solidification.