The invention relates to a drainage hole structure and a drainage method for ditchwater treatment, and particularly relates to a drainage hole structure and a drainage method for ditchwater treatment, which are applied in the field of ditchwater treatment of branch valleys in mountain and valley regions. The invention provides the drainage hole structure for the ditchwater treatment, which has the advantage of high reliability and is used for conveniently overhauling facilities. The drainage hole structure comprises a main drainage hole, a shunting hole, a swirling shaft energy dissipation structure, a high water outlet and a low water outlet. The invention further provides the drainage method for the ditchwater treatment, which has the advantage of high reliability, can be operated for a long time and facilitates overhaul. The drainage method comprises the following steps of (a) judging the situation of a drainage period; (b) draining from the low water outlet through the swirling shaft energy dissipation structure if the drainage period is in a flood season, and draining from the high water outlet through the shunting hole if the drainage period is in a dry season. The shunting hole and the water outlets formed in the drainage hole structure satisfy the requirement of ditchwater drainage in the dry season, the phenomenon that the swirling shaft energy dissipation structure is used as a unique drainage channel for a long time is avoided, and the engineering risk is reduced.