Abstract: In order to study the characteristics of the secondary streamer profile and development mechanism under low pressure and extreme non-uniform field condition, this paper conducted laboratory investigations of 200 mm rod-plane gap AC discharges by low-pressure discharge test platform within 10 ~ 30 kPa. The transition process of primary streamer to secondary streamer under different pressures is obtained, and the initiation mechanism, profile and development characteristics of secondary streamer are analyzed. The results show that the quenching of the primary streamer and its transition to the secondary streamer is caused by the combined effect of stochastic disturbance in the field in front of rod anode and Joule heating due to cathode electron injection. With pressure decreasing, the extension limitation, radial expansion capability and speed of the secondary streamer under an extreme non-uniform field are decreasing gradually. The bifurcation of the primary streamer could significantly decrease the velocity of the secondary streamer. These results have reference value for the study of discharge characteristics of high voltage equipment under low pressure conditions.