The percolation transition behavior occurs in the solid-liquid separation of graphite oxide (GO), which changes the system from suspension to colloid state and terminates the separation process. An indicator of percolation transition is necessary to help control the status of GO suspension to finish the solid-liquid separation process. The swell ratio, macroscopic appearance TEM, and rheological behavior of GO suspension were tested before and after the percolation transition occurred in a specific interval of K+ concentration. Then, the physical properties of 1.00 g/L GO suspension containing 0.40-0.80 g/L K+, including conductivity, thermal conductivity, viscosity, surface tension, and absorbance were characterized. The values of these physical properties showed a sharp change in the specific interval of K+ concentration. We calculated the first and second slope of two adjacent points of each physical property to obtain a proper percolation transition indicator. The conductivity with the second slope up to 500% was the most significant change among these physical parameters, which can be used as an indicator of percolation transition in GO suspension. To verify the availability of the indicator, we explored the percolation transition behavior of Ca2+ and Al3+ in GO suspension and K+ with different GO solid content, found that the conductivity is still the most significant percolation transition indicator. The indicator obtained in this paper is reliable under varying content of GO and types of cations in suspension, which can be used to determine the percolation transition threshold during the solid-liquid separation of GO suspension containing cations.