Abstract: Abstract: The underground granary is an important technical development for building a new system of green grain storage. Compared to the overground granary, the underground granary can make full use of the underground space, which shows significant advantages such as low temperature, loss reduction, eco-friendly environment, land saving, energy saving and safety in grain storage. Currently, such technology is one of the important research interests in the food industry. A new type of underground granary consisting of precast steel plate-concrete composite walls was proposed, and the corresponding mechanical properties of its wall and joints were studied for guiding the design of it. Firstly, two different finite element models of the two pieces of precast steel plate-concrete composite walls with different connecting modes were established with ANSYS software. One model is assumed that the walls connect with a joint, which is modeled as a short steel plate, and another is assumed to be weld together directly without introducing a joint. Their bending and compression properties were simulated and analyzed. Also, in the finite element simulation, Solid 185 element was used to model the concrete part, Shell 63 element was used to model steel plates, and the rigid connection was assumed by arranging common nodes between adjacent elements on the interface of concrete and steel plate. Secondly, the corresponding joint experiments were carried out to verify the simulation results. In the experiment, the steel plate and concrete are connected by bolts in each piece of composite wall. The steel plates of the two composite walls are connected by welding them together with a short connecting steel plate, and thus their connections are assumed to be rigid as well. Practically, in order to simplify the finite element models, the effects of bolts and rebar reinforcements in the real steel plate-concrete composite wall were represented by rigid connection assumptions. Numerical results showed that, for the case of empty granary, which means no internal pressure was applied on the internal surface of the composite wall, the stress concentration occur in the steel plate-concrete composite wall under the external soil and water pressure, but the maximum stress not exceeded the design value, so the prefabricated steel plate-concrete composite wall is safe. During the tests, the separation of steel plate and concrete in each specimen not happened and they worked well as an entire element. Besides, the connecting plate between the two precast steel plate-concrete composite walls looked reliable and no obvious crack damage or excessive deformation. All welding lines kept intact. The numerical results of the maximum deflection along the whole span of the jointless and jointed specimens were 0.7mm and 0.57mm, respectively, and the latter was 18.6% smaller than the former. The numerical predictions of the maximum axial displacement of the jointless and jointed specimens were 1.03mm and 1.01mm, respectively, with a slight difference of 1.94%. Besides, it is observed that the difference between the numerical results and the experimental results was no more than 4% and 10% for the jointless and jointed specimens, respectively. From the comparison, it is concluded that the experimental results are basically same as the finite element results and the established finite element model is verified. Also, the results indicate that the assumption of rigid joint between the two steel plate-concrete composite walls is reasonable. More importantly, it is found that the mechanical properties of the steel plate-concrete composite wall with joint connection are similar to those without joint. Thus, in the practical engineering, the steel plate-concrete composite walls for the underground granary can be mechanically equivalent to the steel plate-concrete composite wall without joint connection. It provides guidance for the design and test of composite wall joint.