We have a SQL server DB, there is a field in a table that store the date as the float type, but we
want to pull the data as the Date type. How can we do that?

I tried cast, convert functions, which work in SQL, but not work in HQL.
I also try to define the field as java.util/sql.Date, hoping it can be converted implicitly, but not working either.

I would greatly appreciate it if you can give me a hint.

I think that you need to implement your custom user type which will convert Java type into SQL type and vice versa. See, documentation about "typedef" tag and org.hibernate.usertype.UserType interface.

Hope this help.