Encapsulation of metal oxide nanoparticles (MO NPs) inside metal-organic frameworks (MOFs) has been realized successfully via surfactant-assisted nano-confined space strategy, which is a universal method for various MO NPs@MOFs. The size of MO NPs was limited by the confined nano-space and could be adjusted to a certain extent. The synthesis mechanism of MO NPs@MOFs was revealed via detailed structural characterizations and a series of control experiments. Surfactants introduced during MOFs (CuBDC, BDC = 1,4-benzenedicarboxylic acid) formation process plays a very important role in producing uniform voids of nano-confined space. Cu ions in MOF frameworks were directly used as precursors to fabricate CuO NPs in these confined void spaces. The synthesized CuO@CuBDC composites showed excellent catalytic activity in C-S cross-coupling reactions and dye pollutant photo-degradation reactions.