The fatigue cracking law of asphalt mixture slabs is investigated based on the APA ( Asphalt PavementAnalyzer) fatigue test,and the representativeness of specimen geometry to actual pavement structure is improved byadjusting the width-span ratio of asphalt mixture specimens. In the investigation,first,unaged,short-term agingand long-term aging slab specimens are respectively fabricated and loaded with a cyclic moving wheel to generatebidirectional bending stress in the opposite-edge supported slab. Then,the deflections of the specimens are measured,the development of fatigue crack is observed,Finally,the fatigue life of specimen is determined at the time itfails.By these fatigue tests,the cracking propagation of a finite-width slab with inherent local defects and underbidirectional bending stress is revealed.The results indicate that the crack tip vertically propagates from the slabbottom to the top and presents a length increase in the horizontal direction at the bottom,and that the crack development,the crack pattern and the deflection curve of the slab specimens are all different from those of beam specimens.