Weak small targets, such as unmanned aerial vehicles, have the characteristic of low flight height, small reflection cross-section and weak thermal information, which are difficult to detect and recognize in low-light-level background by a single imaging method. The visible light, low light night vision, long wave infrared and laser active illuminated imaging experiments were carried out, to study the suitable detection and recognition methods by comparing of weak small target images in different low-light-level background. In the field experiment, the target was a small four rotor UAV with the size of 290 mm×290 mm×196 mm, and the environmental illumination was between 10^-2 lx and 10^-4 lx. The working distance was from 0.5 km to 2 km. The experimental results show that simple visible light system cannot image under 10^-2 lx environment illumination; the recognition distance of low-light night vision and long-wave infrared system is only 0.5 km when the environment illumination is 10^-4 lx; the active imaging method combining near infrared (central wavelength 808 nm) laser illumination and low-light night vision can increase the recognition distance of weak small targets; under the same condition, the active illuminated imaging working distance is 3 times of the dynamic imaging.