In order to investigate the effects of ultrafine-grinding/NaOH synchronous treatment on the separation of wheat straw cellulose, wheat straw was mixed with 6% NaOH solution at a ratio of 0.1g/mL and subjected to ultrafine-grinding/NaOH synchronous treatment with different time. Then, 1.4% acidified sodium chlorite solution and water bath ultrasound was used for cellulose fibers separation. The effects of different treatment times on wheat straw lignocellulosic components and microstructure, crystal structure and thermal stability of separated cellulose were systematically characterized. The results showed that within 0~60min treatment, mechanical force significantly reduced the particle size of wheat straw samples, which effectively promoted the separation of lignocellulosic components. In the separated wheat straw cellulose obtained by ultrafine-grinding/NaOH synchronous treatment, a large amount of micron and nanoscale cellulose fibers was intertwined together. As the treatment time prolonged, the crystallinity of cellulose was firstly decreased and then tended to stabilize after 30~60min. The results of Person correlation analysis indicated that the thermal stability of cellulose was significantly correlated with its crystallinity and treatment time (P<0.05). The research provided important experimental data for the innovative research and development of straw based cellulose materials prepared by mechanochemical synchronous treatment.