We propose to perform neutron diffraction experiments under high-pressure and high-magnetic-field on multiferroic RbFe(MoO4)2 (RFMO) using WISH in combination with a compact-clamp-cell and 14T-magnet. The triangular lattice antiferromagnet RFMO is a well known multiferroic compound. A magnetic field along a axis induces some ferroelectric/paraelectric phases with different magnetic orderings. When pressure is applied above 2 GPa, the crystal structure is changed from trigonal to monoclinic. We anticipate that the 120 degrees magnetic structure in ambient pressure is modified to an incommensurate structure and the field-induced phase transitions are also modified by pressure due to the symmetry lowering. In this study, we investigate pressure effect on the field-induced-phase transitions by neutron diffraction under pressure up to 2.7 GPa and magnetic field 13.5 T with a single crystal.