Abstract: The fracture mode and velocity for the center of marble slab under the stress loading were studied in the experiment. The results are as follows.1. Most cracks cross veins at an angle of about 45° and some nearly 0°. Failures of the rock usually occurred at different time,with one of the cracks first going through the slab. There was shear strain before failure. The direction of the main fracture was in disagreement with the surface of minimum tensile strength. The hydraulic fracturing direction of main fracture is probably in disagreement with the direction of maximum horizontal principal compressive stress.2. logⅤ-L diagram (Ⅴ,velocitv of propagating cracks; L,ratio of crack's length L to (R₂-R₁):R₁ R₂,radius of the indenter and the marble slab,respectively) shows that three stages for the failure of the slab: in the initial,Ⅴ was relatively large (10mm/s) when cracks occurred and then exponentially decreased (0.05mm/s) with increasing L; in slowly fracturing,Ⅴ alternatively increased with increasing L(0.1-2mm/s); and in rapidly fracturing,Ⅴ increased abruptly and a noticed turning might be found,over which log Ⅴ increased exponentially (to 1 m/s) and then fractures occurred.