I AM INSTALLING A SERVICE TO MY BARN, AND THE POWER CO. IS SUPPLING POWER AERIAL TO MY POLE, ON THIS POLE WILL BE THE METER AND AFTER THE METER I WOULD LIKE TO PUT A DISCONNECT ON THIS POLE THEN I WILL BE GOING 400' UNDERGROUND IN CONDUIT TO THE BARN WITH 1/0 CU FUSED AT 70 AMP, AT THE BARN WILL BE A MAIN BREAKER PANEL DO I NEED A GROUND WIRE FROM THE POLE DISCONNECT TO THE BARN OR JUST A GROUND ROD AT THE BARN AND DO MY GROUNDING AND BONDING THERE.

First, please stop shouting. Typing in all capital letters is considered 'shouting,' and makes the post harder to read.

Second .. the barn will NOT have a main panel. The "main panel" is at the meter, where you have that 70 amp fused disconnect. That's where you bond the ground wire and the neutral. So, yes, you get to pull four wires.

Keep the ground and neutral separate at the panel in the barn. Run a wire from the ground bus to the ground rod / ufer, whatever. This is the GEC.

Thank you for the input, also what size ground do i need in that 400' conduit, and i have to drive a rod at both locations right. also can i just put a lug in the disconnect on the pole if the ground wire is to large for the net. block

225.31 & 225.32 Service rated disconnect switch is Required at the Barn.
250.32 A Equipment Grounding wire may or may Not be required.
See 250.32 (B)(2).
If Ground wire is Required Neutral Floats at second Panel.
Where it is NOT required Neutal must be bonded there . in either case a Grounding Electroid is required at the second Building. Read 250.32 (a)
If Ground wire is Required to second panel see 250.122 Adjust for Voltage drop if Phase conductors are upsized.

Yoopersup

Agricultural Building are Exempt from inspection in Michigan , Might not be in your State , If Not read 547.9 2005 If the barn well contain livestock.
Forgot that sorry
yoopersup