The multi-voltage-level DC distribution network (MVL-DC-DN) is a promising network for efficiently integrating rapidly growing DC loads, and fast-growing load demand would bring a challenge to the MVL-DC-DN in terms of the maximum loadability. This paper considers the DC electric spring (DC-ES) as a novel candidate flexible resource for enhancing the maximum loadability of the MVL-DC-DN, and proposes an evaluation method for the maximum loadability. Firstly, with the consideration of device constraints, the impact that the DC-ES on the maximum loadability of the DC distribution network (DC-DN) is analyzed via a simplified equivalent circuit. Subsequently, the power flow (PF) model of an MVL-DC-DN with DC-ESs is established. Finally, a method based on continuation power flow (CPF) for evaluating the maximum loadability of an MVL-DC-DN with DC-ESs is proposed. During the evaluation, limitations of the DC-ES and the DC transformer (DCT) are considered. The consideration of the practical constraints avoids the overestimation of the maximum loadability. The case study verifies the effectiveness of the proposed method.