Hello Jainesh 

Thank you for the solution , i just want to know where i must put this code knowing that i'm a beginner in Odoo .

Hello Garaz

Yes it is possible

start_date = fields.Date(string="Start Date")
contract_start_date = fields.Date(string="Contact start Date", compute="compute_date")

@api.depends('start_date')
def compute_date(self):
self.employee_start_date = self.start_date

I hope this code is helpful for you.

Thanks & Regards,
Email: odoo@aktivsoftware.com
Skype: kalpeshmaheshwari