The contour maps at 17 GHz on the 1992 October 27 solar burst are analysed. Using a nonthermal inhomogeneous model of the radio source, the variations of calculated source size with time are basically consistent with the observation of maps. The variations of calculated brightness temperature with a distance ρ displaced from the project center are in better agreement with the observation of map at 0 1: 45: 29: 889 UT. The calculation shows that the characterizing magnetic field gradient αB at the peak of 17 GHz is about 2, magnetic strength B is about 737G with the magnetic field Bm of the core being 2000 G. However in order to measure the coronal magnetic field accurately, it is necessary to obtain radio-imaging data at more frequencies.