The search for neutrinoless double beta decay (0νββ) process becomes a quite hot topic after the establishment of non-zero neutrino mass by oscillation experiments, as the observation of 0νββ process would indicate the discovery of the new physics beyond the standard model. The EXO-200 is a running detector based on liquid xenon TPC, which is the first 100 kg-class experiment producing results and well demonstrating the key technologies in 0νββ search. The most recent 0νββ half-life sensitivity of 136Xe from EXO-200 has been improved to 3.7 ×1025 yrs at 90% C.L., by combining the data set collected in phase I and phase II. nEXO experiment is extrapolated from EXO-200, aiming to reach 0νββ half-life sensitivity of 1028 yrs by using 5 tonne enriched liquid xenon TPC, which can entirely cover the region of inverted hierarchy. Lots of R&D activities in nEXO are being carried out to enhance the TPC performance. In this proceeding, part of them will be highlighted.