Based on wavelet analysis, fractal theory and ECT (Electrical CapacitanceTomography) technique, a soft-sensing system of gas-solid fluidized bed is established, which can implement the on-line identificatin and the monitoring of the flow regime, and also can measure he voidage of the gas-solid fluidized bed. In this system, wavelet analysis and fractal theory are signals. of pressure flucturation; a 12-electrode ECT system is used to display the flow state and calculate the voidage of gas-solid fluidizd bed by suing a novel image reconstruction algorithm. Experimental results show that the soft-sensing system is effective. It can improve the accuracy of identification of flow regime and can measure voidage of gas-solid fluidized bed with an error less than 5%.