A coaxial reticle alignment device, a lithography apparatus and alignment methods are disclosed. The coaxial reticle alignment device includes: illumination modules (A, B), each configured to provide an alignment light beam; a projection objective (8) under a reticle (5); a reference plate (9) on a workpiece stage (12), configured to carry a reference mark (10); and an image detection and processing module (11) under the reference plate (9). The reference mark (10) is located within a FOV of the image detection and processing module (11), and during movement of the workpiece stage (12), the image detection and processing module (11) receives the alignment light beam having passed sequentially through the reticle alignment mark (6, 7), the projection objective (8) and the reference mark (10), it captures images of the reticle alignment mark (6, 7) and the reference mark (10) which are processed to derive relative positional information between the reticle alignment mark (6, 7) and the reference mark (10) that enables the alignment of the reticle (5) with the workpiece stage (12). The coaxial reticle alignment device adopts dedicated separate illumination means, has a simple structure, allows easy operation and improves alignment efficiency.