Question

Acceleration means non uniform velocity than how can it have uniform acceleration

Answer 1

uniform acceleration means , that the changes in the velocity is uniform

Answer 2

if an object travels in a straight line and its velocity increases or decreases by equal amount in equal intervals of time then acceleration of an object is said to be uniform. for example the motion of a freely falling body is an example of uniformly acceleration motion.
but in Non uniform acceleration velocity of an object changes at non uniform rate.