Hubble constant can be defined as the ratio of receding velocity of an extra galactic object to the distance of that object.
Mathematically,
Hubble constant(Ho) = Receding velocity(v)/distance(d) .
Dimensional Formula of Receding velocity = M0L1T-1
Dimensional Formula of Distance = M0L1T0
Putting these values in the given equation we get,
Dimensional Formula of Hubble constant = M0L0T-1
SI Unit of Hubble Constant is sec-1.