How many permission sets we can assign to one user in Salesforce?

Hello Uday,

One org can hold max of 1000 permission set(1500 including Managed packages) and if we want, we can assign all permission sets to a single User.

You can run the following code snippet in developer Console to check by yourself:

integer count =1;
for(integer i = 1; i<=75;i++){
PermissionSet pr = new PermissionSet(Label='Case Permisson Set'+count,Name='Case_Permisson_Set'+count);
insert pr;
PermissionSetAssignment pm = new PermissionSetAssignment(AssigneeId='<User Id>',PermissionSetId=pr.id);
insert pm;
count++;
}

Hope this helps.!