>
>1)
>
>i just import data from vfp database to sql server,but some filed shows
>'< null >' values, how i will replace with some defalt value for this.

You can create DEFAULT constraint for that field. If it's to late or it doesn't work for you

UPDATE mytable 
    SET myfield = < some vaklue >
  WHERE myfiled IS NULL

>2) >while i m updating the data in sql server, some places the string
>lenght comes more than filed definition
>
>say eg. string lenght 'ABC1234'
>filed length (4), that time i m getting updation failure mesage.
>how will i solve this prob.

You can either increase the size of the field to acomodate data (varchar would be good) or truncate data to fit the field length.