This qualitative study explores how experienced musical theater singers understand and manage the balance between emotional expression and vocal stability during character construction. Data source includes systematic observation, semi-structured interviews and field notes with five high-achieving musical theater soloists from the UK and China. The qualitative analysis of the data reveals a dual influence of emotion and voice, which means that emotions may threaten vocal stability through physiological disruptions but also can enhance vocal expressiveness. To address potential emotional outbursts, singers employ two core strategies: (1) using scientifically grounded vocal techniques to develop various character-related vocal qualities without full emotional immersion, and (2) constructing a dual emotional system during rehearsals that distinguishes between personal and character emotions. The study contributes a practice-based framework for balancing emotional authenticity with vocal safety in musical theater performance.