Many thanks for reply. I mess up the particle's velocity and c_move function. There are relative and absolute movement vector in c_move, in my code I pass the relative vector in c_move, but is that the velocity vector for particle?

Most particle tutorials are using pre-calculate velocity, however I cannot figure out how to attach particle to moving entity.

Edit:
I solved my problem. I just need to divide the length of vector pos2.x, pos2.y, pos2.z by time_step, that's the velocity of c_move relative movement.