The invention discloses an implementation method of high-precision sampling, which comprises the steps of (1) adopting double AD sampling with different dynamic ranges, defining a sampling value witha small dynamic range to be AD1, and defining a sampling value with a large dynamic range to be AD2; (2) multiplying the sampling value AD2 by a dynamic range coefficient, normalizing the sampling value AD2 to the sampling value AD1 to obtain a normalized sampling value AD2; (3) comparing the sampling value AD1 or the sampling value AD2 with a switching constant value, and switching the output ofthe sampling value AD1 or the normalized sampling value AD2 according to a comparison result. The sampling method can ensure the sampling precision under low-end signals with the rated value being 0-10% while meeting requirements of the dynamic measurement range, and thus improves the performance and reliability of the whole high-voltage direct current transmission control and protection system.