The invention discloses an iron based amorphous/alumina ceramic composite powder and a preparation method and applications thereof. The composite powder comprises following components in percentage byweight: 23.2 to 25.2 wt% of Cr, 3.3 to 4.5 wt% of B, 3.1 to 3.8 wt% of Si, 3.2 to 5.6 wt% of Nb, 1.8 to 2.8 wt% of Ni, 10.3 to 12.3 wt% of Mo, 1.5 to 2.0 wt% of Co, 3.2 to 4.2 wt% of Al2O3, and the balance being Fe. The raw materials are added into an induction cooker and then are heated and melted; the melted metals are atomized and dried, then the powder is sieved; the powder is used to preparea wear-resistant iron based amorphous/alumina ceramic composite protective coating, the coating is prepared by an ultrasonic flame spraying technology, and the obtained coating has the advantages ofhigh hardness, good binding strength, and excellent wear-resistant performance and can be used under severe work conditions such as a high parameter valve sealing surface.