An experiment on beat frequency between two independent beams generated by two different types of laser was carried out. One is a wavelength tunable semiconductor laser with central wavelength tunable range of 1052.82～1053.12 nm, and the other is a narrow line width fiber laser with wavelength of 1053.10～1053.20 nm. The foundamental principle of beat frequency signal detection is introduced, and the experimental setup is established. Stable and repeatable beat frequency signal with a period of approximate 10 ns and amplitude of 4 mV is achieved by high frequency oscillograph after amplified by wide-frequency amplifier.Beamsplitting prism and an F-P cavity sweep interferometer are utilized to achieve real-time frequency alignment which can monitor relative frequency shift and measure beat frequency simultaneously. A scheme of auto alignment through computer control is proposed in case of low laser frequency stability.