Nanostructured WC-Co-Al powders with characteristic of in-situ synthesis Al2O3 were synthesized from submicron structured WC-12Co powder and Al powder using ball-milling method. XRD analysis showed that the average size of WC grains was 93.1nm, 39.0nm and 44.8nm after milling 10h, 30h and 50h, respectively. When sprayed by high velocity oxygen fuel (HVOF) thermal spraying, WC-Co-Al powders were more easily flattened than WC-12Co powder without ball-milling. The porosity of WC-Co-Al coating was only 0.57% which was much lower than that of WC-12Co coating with a value of 1.62%. During spraying Al reacted with oxygen, which effectively inhibited the decarburization of WC, and Al2O3 hard ceramic particles were in situ generated in coatings. The microhardness of WC-Co-Al coating was 1298?3HV0.1, higher about 36% than that of WC-12Co coating, which mainly benefitted by the enhancement effect of Al2O3 particles, nanocrystallization of WC phase and lower porosity.