Abstract: A MXene membrane with gradient pores, its preparation method and application are provided. The MXene membrane with gradient pores, excluding the substrate, includes the following layers in sequence from bottom to top: an ultra large pore MXene membrane layer with a thickness of 0-30 nanometers (nm) and a pore size of 2-5 nm; a large pore MXene membrane layer with a thickness of 0-30 nm and a pore size of 0.9-1.2 nm; a medium pore MXene membrane layer with a thickness of 20-50 nm and a pore size of 0.6-0.8 nm; and a small pore MXene membrane layer with a thickness of 40-60 nm and a pore size of 0.3-0.5 nm. The present disclosure prepares the MXene membrane with gradient pores by repeating spin-coating and plasma irradiation while limiting the irradiation time.