A fingerprint image acquisition device includes: a light source, a finger touching surface, a convex lens, an image sensor and a grating. The light source is a surface light source, and the grating is disposed on a light output surface of the light source. The light source is configured to emit a light beam, the grating is configured to change a propagation direction of the light beam to form a detection light beam, the finger touching surface is configured for a user to place a finger thereon to reflect the detection light beam and thereby obtain a reflected light beam, the convex lens is configured to focus the reflected light beam on the image sensor, and the image sensor is configured to generate a fingerprint image based on the focused reflected light beam. Accordingly, the invention can make the structure of the fingerprint image acquisition device be more compact.