Proteins are crucial to most biological processes,such as enzymes,and in various catalytic processes a dynamic motion is required.The dynamics of protein are embodied as a conformational change,which is closely related to the flexibility of protein.Recently,nanopore sensors have become accepted as a low cost and high throughput method to study the features of proteins.In this article,we used a SiN nanopore device to study the flexibility of T7 RNA polymerase (RNAP) and its complex with DNA promoter.By calculating full-width at half-maximum (FWHM) of Gaussian fits to the blockade histograms,we found that T7 RNAP becomes more flexible after binding DNA promoter.Moreover,the distribution of fractional current blockade suggests that flexibility alters due to a breath-like change of the volume.