The saturation spectroscopy of the 811 nm 2P3/25p[5/2h-2p3/25s[3/2]2 line of metastable krypton atom was used to lock the frequency of a Ti:Sapphire laser. Two kinds of frequency modulation method were utilized, one using an electro-optic phase modulator, the other using an acoustic-optic frequency shifter. When the feed-back loop was closed the frequency drift was reduced to 1 MHz, while it was about 8 MHz when the loop was open. The laser can be frequency stabilized during hours-long measurements and it allows us to realize laser cooling and trapping of the different isotopes of krypton. Key words: laser technique; laser frequency locking; saturation absorption spectroscopy; frequency modulation; krypton atom; cold atom