Modular multilevel converters (MMCs) are increasingly employed in modern high-power applications. To utilize the advantages of this converter topology, modulation scheme is crucial and needs to be properly selected and designed. Phase-shifted pulse-width modulation (PS-PWM) is extensively adopted by MMCs for its good harmonic characteristics. Regarding the design of PS-PWM, the phase shift angles between submodules (SMs) or converter arms can be properly selected to achieve a good waveform quality of MMCs, and their selection methods are well established in the literature. However, the carrier initial phase angle (CIPA) has long been neglected, while it also has a significant impact on the harmonic profile of line quantities of MMCs under certain conditions. This paper aims to reveal and analyze the above effect of the CIPA for an MMC with PS-PWM. For an efficient design of PS-PWM with properly determined CIPA, simplified numerical emulation is employed instead of the conventional time-consuming simulation. Effectiveness is verified through simulations.