As the particle is falling down its potential energy (U=mgh) is decreasing as the height of the particle from the ground is decreasing. But at the same time, the velocity of the particle is increasing as it is falling under the action of gravity. So, the particle has an acceleration g. Therefore, the kinetic energy (T=12mv2) of the particle is increasing.
The loss of potential energy=The gain of kinetic energy
Therefore, in this process, the conservation of energy is not violated.