High-quality carbon nanotubes (CNTs) are promising materials in many applications. However, current chemical vapor deposition (CVD) methods for CNT synthesis suffer from the discrepancy between the quality and yield of CNTs: Low-quality CNTs can be synthesized with high yield, while high-quality CNTs can only be synthesized with low yield. Here a CVD method has been designed to synthesize both high-quality and low-quality CNTs using the same combination of catalyst and precursor. As a result, we were able to understand the reasons for the low yield in high-quality CNT synthesis and a method was derived to improve their yield. This understanding is an important step towards high-yield synthesis of high-quality CNTs.