This purpose of this study is to examine the acoustic characteristics of Russian glide /j/ and vowel /i/ through the size of the cross-sectional area of constriction of these sounds. First, the structural difference between /j/ and /i/ is investigated through the tube model of the source-filter theory, and then the F1 and size of the cross-sectional area of constriction of the two sounds is obtained through the pronunciation of a Russian native speaker, and based on these data, I tried to suggest the acoustic characteristics of the Russian glide /j/, which is distinct from the vowel /i/. According to the tube model of the source-filt theory, the glide /j/ and vowel /i/ belong to the threetube model, and unlike the vowel /i/, the glide /j/ has a catenoid shape, indicating the transition process of the glide /j/. And looking at the F1 of the /i/ and /j/ revealed in the table 2 and 3, the size of F1 decreases as the volume of the posterior cavity increases in both sounds, but it can be confirmed that the F1 of /i/ is higher than /j/ at the same location. Unlike the vowel /i/, the F1 of the glide /j/ has different sizes depending on the following vowel /e, a, o, u/, so it is reasonable to examine them by series /je, ja, jo, ju/. For Russian female speakers, it can be seen that the average F1 of the vowel /i/ is 380 Hz, and the average F1 of the glide /j/ is 271.40 Hz in /je/, 318.93 Hz in /ja/, 261.47 Hz in /jo/, and 241.13 Hz in /ju/. And it was found that the size of the cross-sectional area of constriction of the Russian vowel /i/ is 0.351 cm2, and that of the glide /j/ is 0.152 cm2 in the /je/, 0.256 cm2 in the /ja/, 0.133 cm2 in /jo/, and 0.095 cm2 in the /ju/ series. Since the size of the cross-sectional area of the constriction of the glide /j/ is smaller than that of the vowel /i/, it can be said that the Russian glide /j/ is out of scope of the vowel, and considering that the size of the supraglottal constriction of the unvoiced fricatives /s/ and /š/ is 0.05 to 0.15 cm2, it was found that the size of the cross-sectional area of the constriction of the glide /j/ of the /je/, /jo/, and /ju/ series, has an acoustic characteristic close to that of a Russian fricative. And it was found that the fricative phenomenon caused by the narrow constriction of the glide /j/ is well reflected in the waveform and spectrogram of the glide /j/, and in the sound wave of the Russian glide /j/, a non-periodic sound wave of turbulent noise is seen, in addition to thiese, F1 cutback, partial peach cutback, and the relatively weak intensity of the turbulent noise portion were also observed in the Russian glide /j/.