The invention relates to a method and a system for high-accuracy simultaneous observation of a long air gap. The method comprises the following steps of: employing an optical observation system and an electrical measurement system, wherein the optical observation system comprises a static-state optical imaging device and a high-speed imaging device; and the electrical measurement system comprises a current measuring device, an electric field measuring device and a voltage measuring device; triggering the high-speed imaging device and the static-state optical imaging device by using a high-speed trigger and controlling the two devices to take photos, and obtaining the photos by a high-speed camera through a network cable via a computer; synchronously triggering the high-speed imaging device and the static-state optical imaging device by means of the high-speed trigger, and outputting the exposure clock signal and an imaging start recording signal of the high-speed imaging device through a coaxial cable; and triggering a high-speed storing/recording device by using the imaging start recording signal to record all electrical signals. The system is composed of the static-state optical imaging device, the high-speed imaging device, a transient-state electric field measuring device, a discharge current measuring device, a discharge voltage measuring device, a high-speed data memory device and the high-speed trigger.