Abstract: A non-template chemical vapor deposition (CVD) method was adopted to prepare highly directional and self-standing aligned carbon nanotube (ACNT) arrays on a quartz substrate on a large-scale and H2O2 was used to in-situ oxidize impurities in the arrays. It is found that the in-situ purification of ACNT arrays by H2O2 is an efficient way to purify ACNT arrays without damaging their alignment and the ACNT arrays obtained have a different thickness. In most cases the tips were open with a smaller amount of amorphous carbon, disfigured CNTs and other impurities. Such arrays have potential applications in field emission. The results of Raman spectroscopy and TGA show that the crystallization and thermal stability of ACNT arrays increase after the purification.