3J40 alloy is a kind of high-strength， high-hardness， wear and corrosion-resistant alloy with high Cr and Al content used in precision instruments industry. This paper studies the deformation process and failure mechanism of 3J40 shaft tine under compressing load based on a failure analysis case in which 3J40 shaft tine and red corundum compress with each other. The crack and fracture morphology were investigated by stereoscopic microscope and scanning electron microscope （SEM）. The stress distribution and failure mechanism were also analyzed for shaft tine serving state using finite element analysis. The results indicate that the spherical surface of 3J40 shaft tine was compressed to a plane under compressing load of red corundum surface， forming a Φ220 μm plain zone. The shaft tine fracture is ductile， and the shear stress peaks at the contacting rim of shaft tine and plane. Thereafter cracks form at the shear source and expand in axial direction and then turn around 90° at waist zone of the shaft tine. Theoretical estimation and finite element analysis were conducted based on Hertz contacting theory. The results show that large shear stress and strain exist in the 3J40 material which results in a shear failure mechanism. The results are significant for the performance optimization and structure design of shaft tine materials.