This paper studies relations of F1, F2, and F3 of vowels, spoken at reading speed by 3 speakers of 2 languages (Yi and Mandarin Chinese). The results show that vowel Formants keep stable relation of Logarithmic Quotient (Z value, Z1=log F2/log F1, Z2=log F3/log F2). The ratio of Standard deviation and Average keeps below 3% for most vowels. Varying degree keeps below 3% for different speakers. This paper proves that Logarithmic Quotient is an ideal vowel-normalizing model and has potential applications in speech recognition and speech comparison.