A method for preparing an upconversion-luminescence flexible hybrid membrane for visual detection of tumor markers is provided. Metal ion doped black phosphorus quantum dots (M-BPQDs) are prepared by adopting ultrasonic and solvothermal processes; mesoporous SiO2 grows on the surfaces of the M-BPQDs and amination modification is performed; the M-BPQDs are connected with carboxylated single-stranded DNA1; receptor molecules enter pores; single-stranded DNA2 aptamers and the DNA1 are combined due to base complementation to encapsulate receptors in the pores; and an M-BPQDs probe is prepared. DNA1 terminal-SH and a composite membrane are formed by assembling polymethyl methacrylate-polyimide-gold nanoparticles in a layer-by-layer manner bound by Au—S bonds, and the membrane and the probe are connected to construct the flexible hybrid membrane. The new flexible hybrid membrane is simple and inexpensive to prepare and is highly sensitive.