I blew a fuse in my rider mower model 917254661,when I went to install new fuse it blew right away the key is in the off position scratching my head here

Trace your wires.. one of them has the insulation rubbed off and its shorting out the chassis someplace. You can then wrap that area with electrical tape and tie off the cable so it doesn't continue to rub.

I traced them all and its still doing the same thing,I replaced Ignition switch and solonoid plus the positive cable to the battery

You have a short to ground someplace, on one of the other smaller wires... the only way that fuse blows is a current larger than its rating is attempting to go through it. There should be ZERO current going through it with it turned off. Even when its on run you should not have that much current draw. That is indicative of a short. And they aren't necessarily obvious, particularly on dirty and crusty wires. I still think you missed something when you went through it last time. Check your safety interconnect wires and switches as well (like under the seat and on the clutch/brake)... make sure the wires are good and a switch hasn't come loose and is touching something.

What were you doing when the fuse blew? Was the engine running?

Engine wasn't running key wasn't turned on

Sounds like a short to me. Try disconnecting the solenoid and test with a new fuse. Fuses are cheap and you may go through several as we experiment. If the fues does not blow with the solenoid disconnected then tap the hot cable back on the solenoid, did it blow?