if i get iit in josaa 7th round can i participate in csab for nit,please say me i have very less time
No, if you confirm and accept the seat in IIT or NIT, in any round of JOSAA, be it first or last, you cannot apply for CSAB in that Case. CSAB clearly states, one should not have any seat allotted through Josaa.
For more information do follow the link below