Observations of interplanetary slow shocks near 1 AU are rare. From the magnetic field data obtained from MFI and the proton and electron data obtained from SWE of the WIND spacecraft, we identify the observation of a reverse slow shock on December 24, 1994. The plasma &bgr; is small in preshock region. A new method is introduced to determine the best-fit solutions for both the normal of the shock surface and the coplanarity plane when the total deviation of the observed magnetic field and velocity vectors from the theory reaches a minimum. The flow conditions on both sides of the slow shock agree well with those predicted by MHD shock theory. ¿ American Geophysical Union 1996