The invention provides a semiconductor laser pump single longitudinal mould and a frequency laser and further expands a frequency selection mode of a torsion pendulum cavity. Resonant cavities of the frequency selection mode are used as two resonant cavities, so that two signal longitudinal moulds can respectively oscillate in the respective resonant cavities, fundamental frequency waves of the two signal longitudinal moulds meet by the resonant cavities, a nonlinear crystal is inserted into the overlapped area of two sub-resonant cavities to obtain signal longitudinal moulds and a frequency laser source which are different from signal-frequency double-frequency laser, and signal longitudinal mould output light with more wavelengths can be obtained by selecting different gaining media.