Spontaneous chiral symmetry breaking and mass gap of QCD in finite volume

We present the lattice QCD simulation with the 2+1+1 flavor full QCD ensembles using near-physical quark masses and different spatial sizes $L$, at $a\sim$ 0.055 fm. The results suggest that spontaneous chiral symmetry breaking is effectively restored at $L\le 1.0$ fm, while the gap between the nucleon and pion masses remains.