A theoretical study of the quality and the validity range of different numerical and analytical methods of calculating of the frequency shift in measurement using microcromechanical sensor is presented. This work considered a calculating method for natural frequency in comparison with experimentally measured oscillation frequencies of microcromechanical sensor immersed in air and/or viscous medium. The numerical methods for solving the equation of resonance oscillation of the console fixed on one side are considered for calculating the natural oscillation frequencies of standard AFM cantilevers.