This paper describes a novel technique to analyze the response of multi-harmonic thickness shear mode (MTSM) sensor. In this method a MTSM sensor was operated not only at its fundamental frequency (5 MHz) but also at the 3rd, 5th, and 7th harmonics. Then the ratios of the changes in the resonant frequency of motional arm for the harmonics were calculated and compared with the ratios of the penetration depths of acoustic waves at the same harmonics. These comparisons showed that if the main cause of the frequency shifts of the harmonics is because of the mass loading, these two ratios are equal each other.