The mode-selecting principle of a F-P interferometer and experiments of mode selection and mode-locking of a laser diode with an external F-P interferometric cavity are demonstrated and reported for the first time. The septic and dynamic single internal-mode operation is realized by using a PZT to adjust the interval of the F-P interferometer.The nearly transform-limited Gaussian pulses with a repetition rate of 656 MHz and pulse width of 13 ps have been obtained. The time-bandwidth product is 0.46. At last the effect of a F-P interferometer on the lasing mode of diode lasers is discussed.