Is it possible to have rainbow at night?

It is possible.
A full moon is bright enough to have its light refracted by raindrops just as is the case for the sun. Moonlight is much fainter, of course, so the lunar rainbow is not nearly as bright as one produced by sunlight. Lunar rainbows have infrequently been observed since the time of Aristotle or before.

By the way, Are u doing hw of weather today? hahahahaha

夜晚無光?

It isn't possible to have rainbow at night because rainbow can only be found if has sunshine after rain.
The sun rises only at day time, but not night time. Although it rains at night,there is no sunshine.Therefore, the lights cannot be refracted and rainbow doesn't appear.