The quantum spin magnet NH4CuCl3 is an antiferromagnetic dimer system, which has a magnetic ground state, and shows two-stepped magnetization plateaus. The origin of the plateaus and the detailed spin structure is not well understood. We have investigated the NMR spectra of deuterated ND4CuCl3 in the field region of the first plateau. Resonance peaks of the Cl-NMR spectra are classified into two groups with different temperature dependences. This indicates the existence of magnetically inequivalent dimers which are localized in space. Rotation profiles of the 2D-NMR spectra show many small peaks, indicating that the NH4 molecules are oriented in a finite number of directions.