Carbon nanotubes (CNTs) have been utilized in various applications, including drug delivery and energy conversion. It is essential to elucidate the underlying transport mechanism across cell membranes to understand their role as drug-delivery agents. Molecular dynamics (MD) simulation is a powerful tool for investigating such transport mechanisms. In this study, we demonstrate the spontaneous translocation of CNTs across a model membrane using the weighted ensemble (WE) method in conjunction with an all-atom MD simulation approach. Two CNTs with similar diameters but differing lengths are employed to uncover the transport mechanism and compare their translocation efficiencies. Both CNTs rapidly penetrate the hydrophobic core of the model membrane; however, they exhibit distinct behaviors when translocating through the lower leaflet of the membrane.