Abstract: In the laboratory simulation of a small square pipe with a single head, a micro thermocouple, an ion current sensor and a flame optical signal sensor were used to test the change of temperature, ion current intensity and velocity during the two conditions of the ignition of the top and the 400mm position at the top of the distance. The experimental results show that: When the ignition occurs at the top 400mm position, the temperature is higher during the propagation of the flame to the closed end, and the highest temperature in the pipe is greater than the maximum temperature of 623K at the top of the ignition. The velocity of the flame propagating to the two sides of the pipe produces a difference of several times, the maximum velocity to the closed end is only 0.89m/s, and the speed of spreading to the outlet reaches 20 m/s, less than the speed 33.33m/s at the exit at the top of the ignition. The peak value of ion current propagating to the closed end is 0.03μA, while the peak value of ion current reaches 0.38μA at the top ignition. At the top of the ignition, the velocity of the flame spread in the pipe and the peak value of the ion current are large. It shows that the combustion reaction of the premixed gas flame at the top ignition is more intense.