This paper studies the feasibility and contribution of a ASLIP model for spinal quadruped robot’s locomotion control. We simplify the spine of a cheetah into three segments and two joints by imitating the fragmental function of the skeleton. Next, we propose that the alternating locomotion of the leg and the virtual leg during stance phase will enlarge the leg’s movement range, where we define the leg is connecting the toe and the shoulder/hip joint, and the virtual leg is connecting the toe and its near spine joint. Then, control those legs based on SLIP, and there exist two springs that locomotion alternately during one stance phase. The passive dynamics of ASLIP model is studied, and the result shows that the ASLIP provides a wide speed adaptation region, which means it can adapt to higher speed in the case of not changing touchdown angle. Besides, the ASLIP evidently has lower maximum GRF than those SLIP model under the same conditions.