Langmuir probes and Faraday cups have been used to characterize electron cyclotron resonance plasmas which have been used in the depositions of GaN films on the substrate of (0001)α-Al2O3.These plasmas were generated with microwave power(Pw) from 300W to 1100W at pressures(p) range from 0.8Pa to 0.05Pa using N2 as the plasma source.The relationship between the plasma parameter,such as ion density(Ni),electron temperature(Te),plasma potential(Vp) and ion current density(Ji),and system parameters,such as pW and p,is given.And the axial and radial distributions of Te,Ni,Vp and Ji are presented.The growth rate and the quality of the GaN film strongly depend on the growth condition.The higher the plasma density,the higher the N/Ga ratio of GaN film.When the microwave power was 850W and gas pressure was 0.22Pa,the plasma near the substrate was characterized by a Te near 1.4eV and plasma density near 2.0×1011 cm-3,and the growth rate of GaN was as high as 0.9μm/h.The full width at half maximum of double-crystal X-ray diffraction rocking curve is 16 arcmin.