The effect of heat treatment time and temperature the interfacial reaction between NiCrAlY coatings and Ti3Al substrates have been investigated. The Ti3Al substrates were coated with catholic arc ion plated NiCrAlY and then heat treated in vaccum at different temperature and length of time. SEM observation and EDS、EMPA、XRD analysis results showed that:there were great difference in the interfacial reaction between under and above 870℃.Typical solid reaction occurred after heat treatment at 870℃or above. An investigation of the interfacial reaction suggested that the decisive factors were different at different temperature period and at different part of the interface.