ln physics, the process of coupling laser beams into a Fabry-Perot( FP) cavity is described asimposing boundary condition on the traveling optical field.Thereby ,the output optical beams become a series ofdiscrete laser modes from the F resonator. In general, laser modes are categorized into transverse andlongitudinal( or axial) eigenmodes.In order to provide a more intuitive understanding of the boundary-yalueproblem about the laser beam propagation inside the FP resonator, we describe in detail a physics lab coursefor the study of laser modes from a FP cavity for undergraduates at the School of Physics , Huazhong Universityof Science and Technology.To fully characterize the laser modes from a FP resonator, three experiments as aseries are designed,including:(1) a study of transverse mode from the PP cavity through the measurement ofbeam waist of the fundamental mode; ( 2) the measurement of free spectral range to characterize thelongitudinal modes;and(3) two independent methods to measure the FP cavity linewidth and cavity finesse forthe longitudinal mode characterization using the transmitted signal and the reflected PDH signal.The intendedaudience includes both undergraduates who have studied Optics , Lasers , Optoelectronics and other related courses , and researchers pursing a preliminary understanding of frequency stabilization technology based on areferenced FP cavity.