Dear Dezheng.Zhu,
A similar question was asked and answered in the following forum topic: FAST_v8.15 OutList parameters - #2 by Jason.Jonkman.
If the generator or drivetrain DOFs are enabled in ElastoDyn, I would expect large differences in the derivatives calculated from a linearization analysis between RotPwr from ElastoDyn and RtAeroPwr from AeroDyn because the former is effected by rotor acceleration/deceleration while the later is not. If the generator and drivetrain DOFs are disabled in ElastoDyn, then I would expect quite good agreement between the two.
Best regards,