Abstract: Cracking mechanism is explored of WC based high Mn steel-bonded carbide which is composed of w(WC) 75%~90%,w(Mn):w(C)≥10, w(Ni)3.0%~5.0% and Fe balance. Based on magnetic measurement, X-ray diffraction energy spectrum analysis and electron microscope scanning, it is confirmed that change of composition and metallographic structure are responsible for the brittleness and work-unhardening for magnetic alloy, while the nonmagnetic alloy has evident work-hardening effect. Further research result shows that the magnetism is stronger for the alloy with coarser grain WC, so magnetism could be regarded as an index to judge the usability of the alloy.