  We report the first Very Long Baseline Array (VLBA) observations of 43 GHz
v=1, J=1-0 SiO masers in the circumstellar envelope of the M-type semi-regular
supergiant variable star AH Sco at 2 epochs separated by 12 days in March 2004.
These high-resolution VLBA images reveal that the distribution of SiO masers is
roughly on a persistent elliptical ring with the lengths of the major and minor
axes of about 18.5 and 15.8 mas, respectively, along a position angle of
150^{\circ}. And the red-shifted masers are found to be slightly closer to the
central star than the blue-shifted masers. The line-of-sight velocity structure
of the SiO masers shows that with respect to the systemic velocity of -6.8 km/s
the higher velocity features are closer to the star, which can be well
explained by the simple outflow or infall without rotation kinematics of SiO
masers around AH Sco. Study of proper motions of 59 matched features between
two epochs clearly indicates that the SiO maser shell around AH Sco was
undergoing an overall contraction to the star at a velocity of ~13 km/s at a
distance of 2.26 kpc to AH Sco. Our 3-dimensional maser kinematics model
further suggests that such an inward motion is very likely due to the
gravitation of the central star. The distance to AH Sco of 2.26$\pm$0.19 kpc
obtained from the 3-dimensional kinematics model fitting is consistent with its
kinematic distance of 2.0 kpc.
