The single walled carbon nanotube (SWCNT) cloning or its seeded growth with a catalyst particle docked on one of its ends was proposed as the ultimate solution for chirality-specific SWCNT synthesis and, therefore, revealing the effect of catalyst particle size on the robustness of the SWCNT cloning is crucial for experimental designs. Through systematic atomic simulations, we have clearly demonstrated that the robustness of SWCNT cloning depends on both the chiral angle of the SWCNT and the ratio of the diameters between the SWCNT and the docked catalyst particle. The zigzag (ZZ) or near ZZ SWCNTs are highly sensitive to the size of the docked catalyst particle. A small change of the catalyst particle size could lead to a variation of the SWCNT's chirality. In contrast, armchair (AC) or near-AC SWCNTs are less sensitive to the size of the docked catalyst particle and able to maintain their original chiralities within ∼30% variation of the catalyst particle size. This study greatly deepens our understanding of SWCNT's growth mechanism and provides a quantitative guidance for SWCNT cloning.