Abstract: A high-speed data acquisition system for multi-cylinder spark ignition engine was developed in order to measure the indicator diagrams of each cylinder simultaneously with the maximum sampling frequency of 1 MHz and the total input signals of 16 channels at the same time. A carburetor S. I. engine reconstructed into a double fuel engine has been tested using the data acquisition system in this research. At lease 50 cycles' pressure data of each cylinder were measured. The average value and the fluctuant coefficient of maximum pressure were calculated. The comparison a-mong different cylinder's inlet air quantity has been made using the maximum pressure's average value. Then the combustion pressures of each cylinder have been measured continuously and simultaneously on condition that either burning gasoline or compressed natural gas (CNG). The comparison of combustion and variation among each cylinder has been made using the averaged value and the variation coefficient of the maximum combustion pressure. The experiment results show that the variation coefficient of the maximum combuction prossure when burning CNG is lower than the value of gasoline engine.