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Hybrid bulk acoustic wave and surface acoustic wave (BAW/SAW) devices attract extensive interests due to their high electromechanical coupling coefficient and quality factor. In this study, longitudinal BAW coupled SAW resonators with piezoelectric AlN inter-digital transducers (IDT) were simulated and fabricated on diamond substrates to increase the working frequency as well. The simulated figure of merit value is 104, 123 % improved comparing with the corresponding metal IDT of 46.5. The frequency response spectrum of single port reflection (S11) shows dominant harmonic resonance at 913 MHz with electromechanical coupling coefficient of 2.16 % and quality factor of 913. These results indicate mutual transductions between BAW and SAW occur with sufficient efficiency in hybrid structures, which is analyzed and interpreted by equivalent acoustic impedance theory. [Display omitted] • Diamond based longitudinal BAW coupled SAW resonators were designed and fabricated. • High figure of merit and working frequency can be achieved for the SAW devices. • The simulated figure of merit value is 104 on an Ag/AlN/Mo/Diamond/Si structure. • 913 MHz resonance with bandwidth of 2.16 % and quality factor of 913 was observed. • BAW-SAW mutual transduction is analyzed by equivalent acoustic impedance theory. [ABSTRACT FROM AUTHOR]