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In high-altitude regions, printed circuit boards are affected by both low pressure and contamination, which may lead to discharge and even the failure of electrical devices. From the viewpoint of safety and reliability, it is necessary to investigate the effects of the pressure on tracking failure of contaminated printed circuit boards. However, the tracking failure is a nonlinear and indeterminate process which results in the dispersity of experimental results. This paper proposes two nonlinear methods, including fractal dimension of tracking pattern and recurrence plots of discharge current, to analyze the phenomena and mechanism of tracking failure under reduced pressures. The experiments were carried out in a decompression chamber, with the pressure reducing from 102.74 kPa to 0.6 kPa. The test sample was made by printing a pair of copper foil electrodes onto a glass-cloth-base epoxy resin laminate with the insulation distance from 500 Â¿m to 100 Â¿m. The contamination was simulated by a droplet of NH4Cl electrolyte with the resistivity of 4 Â¿Â·m. The time to tracking failure, the fractal dimension of tracking patterns and the recurrent plot of discharge currents were obtained as functions of the pressure and the insulation distance. The results reveal that the nonlinear methods can give a good identification of the surface morphology and the underlying mechanism in the tracking test. Effects of the pressure and insulation distance on the tracking failure were quantitatively reflected with the fractal dimension of tracking patterns and the recurrent plot of discharge currents.