Abstract: Carbon-based phosphotungstic acid (H3PW12O40) catalyst was prepared from sawdust of Chinese fir by in-situ synthesis. Nanocrystalline cellulose (NCC) from cellulose by catalytic hydrolysis was studied. The effects of impregnation ratio, carbonization temperature and carbonization time on the yield of NCC were also analyzed. The results showed that under the impregnation ratio of liquid to solid 2.5:1, thecarbonization temperature 350 ℃ and carbonization time 1.5 h, a comparatively high yield of NCC was observed as 25.28%. The catalysts were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscope. The results indicated that phosphotungstic acid was loaded on the carbon under good conditions, the keggin structure characteristic absorption peak of carbon-based phosphotungstic acid remains stable, and the initial decomposition temperature of keggin structure of phosphotungstic acid is 370 ℃. The morphological and crystal structures of NCC were carried out by Transmission electron microscopy and X-ray diffraction. The results showed that the NCC observed by TEM turned out to be rod-like, with the size of 9-70 nm in width and 130-830 nm in length and the average aspect ratio of 11.2:1. X-ray diffraction analysis revealed that the crystallinity of the NCC was 76.1 %, with the average particle size of 6.9 nm.