For example I’d like to make small rain drops after interact with ground.
Thank you
Your best bet would be to set the ground as a collision object under the physics panel. If you want the raindrops to vanish after the hit the ground, make sure that “die on hit” is checked.
I don’t want vanish.
I’d like to divide particles to two or three after hit on the ground.
It does not look like the 2.64 particle system can do that. I seem to remember that the 2.49 had a feature called spawn children upon death. Which might have worked in this situation but it seems to have been removed.
Essentially you need fireworks. After the initial launch the particle changes into something else. (upon collision in your case).