A vertical-structure photodetector based on two-dimensional perovskite (PEA)₂(MA)₄Pb₅I₁₆[PEA is C₆H₅(CH₂)NH₃, MA is CH₃NH₃] is fabricated and its property is analyzed. The photocurrent of the device reaches a maximum when the thickness of the two-dimensional perovskite thin film is 280 nm, while at 500 nm, the external quantum efficiency reaches 90%, the responsivity reaches 0.37 A/W, and the detectivity reaches 3.4×10¹² Jones(1 Jones=1 $\mathrm{c}\mathrm{m}?\mathrm{H}{\mathrm{z}}^{\mathrm{1}/\mathrm{2}}/\mathrm{W}$). The response time of the device does not continue to decrease as the thickness of two-dimensional perovskite thin film decreases, but reaches a minimum at the thickness of 80 nm due to the effect of carrier transit time and the quality of perovskite thin film. By fixing the thickness of the two-dimensional perovskite film at 80 nm, we finally achieve a response time of 113 ns by reducing the effective area of the device. This work is of great significance to promote the development of low-cost and fast-response photodetectors.