serene

serene
/sɪˈri:n; sə`rin/ adj
calm and peaceful; tranquil 平静的; 宁静的: a serene sky 晴朗的天空
    a serene look, smile, etc 安详的神情、 笑容等
    In spite of the panic, she remained serene and in control. 尽管人心惶惶, 但她却泰然自若.

牛津英汉双解词典