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Instability of impinging sheet is analyzed for power-law fluid by solving dispersion equations deduced based on a simplified linear model under anti-symmetric and symmetric disturbances in present work. An impinging atomization platform is established, and experiments for gelled power-law simulant are accomplished. A comparative analysis between experimental and linear results is conducted. Relative conclusions indicate that anti-symmetric disturbance is superior to symmetric disturbance in instability of the sheet. Increasing sheet velocity or decreasing sheet thickness can accelerate instability, but the disturbance of sheet is suppressed by promoting consistency and flow index. Experimental impinging sheets are divided into four modes and their distributions are also identified. Besides, spray angle increases, but breakup length and dominant wavelength decrease with increasing jet velocity and impinging angle. By comparison, experimental breakup lengths of 75° impinging angle relatively accord with theoretical ones. Theoretical breakup lengths are lower than experiments at lower sheet velocity but have an opposite trend at higher sheet velocity when impinging angle is 90°. As to dominant wavelengths, linear analysis shows an acceptable overestimation compared to experiment. In spite of some discrepancies, linear analysis developed at present can be used to predict the breakup characteristics of gelled power-law sheet.