Two-dimensional material tungsten diselenide (WSe2) nanosheets are coated on a microfibre knot resonator (MKR) to achieve an all-optical power modulation functionality. On account of the strong absorption property of WSe2 and the resonance enhancement properties of MKR, the transmitted optical power of signal light within the WSe2-based MKR can be effectively modulated. The sensitivities of light–control–light experiments with 405- and 660-nm lasers are as high as 0.32 and 0.12 dB/mW, respectively. The sensitivities and power tuning can be enhanced by a higher resonance Q and a larger extinction ratio of MKR. In terms of the response time, the average rise and fall times are 3.5/3.7 and 3.5/4 ms with 405- and 660-nm lasers, respectively. This proposed structure is expected to achieve potential applications in all-fibre-optic–based tunable device such as optical modulator, detector, and so on.