Streamer performance is the main mechanism of long air gap discharge; the inception characteristic of streamer has been widely used in engineering. The streamer inception characteristic under DC voltage has been researched by many researchers, but the characteristic under impulse voltage especially under lightning impulse voltage with large voltage rise rate has been studied rarely. The inception characteristics of streamers in 1m rod-plane air gap energized by positive lightning impulse voltage have been researched. The new diagnosis of streamer inception has been given, and the streamer inception voltages and electric fields under different electrode and voltage rise rate have been recorded. According to experiment results, the streamer inception electric field criterion considering voltage rise rate has been proposed. The criterion in this paper is also be verified for widely parameter ranges.