Great emphasis has been placed on the development of GHz femtosecond lasers for the Yb-doped All-Solid-State Laser(ASSL) that has important application values in many fields such as precision measurement. Compared to general femtosecond oscillators with repetition frequencies in the tens to hundreds of megahertz,GHz femtosecond pulse has been demonstrated to have larger spacing between adjacent longitudinal modes and higher single longitudinal mode power. This GHz repetition frequency femtosecond oscillator is realized by passive mode-locking techniques, including Semiconductor Saturable Absorption Mirror(SESAM) and Kerr Lens Mode-locking(KLM). The latter has the following advantages: simplicity, very fast response, self-starting and self-sustaining. Ytterbium-doped gadolinium calcium chlorate (Yb:CaYAlO₄, referred to as Yb:CYA) crystal has the advantages of easy growth, broad and flat gain curve, high specific heat capacity, good thermal conductivity, etc. It is an excellent dielectric crystal for generating femtosecond ultrashort pulses.Femtosecond laser pulses based on Yb:CYA crystals were first reported in 2011. In 2018, MA Jie et al. of Jiangsu Normal University reported that the shortest pulse width of Yb:CYA oscillators was 21 fs with the help of two SF10 prisms, while the highest output and peak power achieved by Yb:CYA crystals was experimentally realized by TIAN Wenlong et al. from Xidian University. The Yb:CYA optical frequency comb debuted in 2016, demonstrating the first Kerr lens mode-locked solid-state optical frequency comb in the 1 μm band. In 2019, the author's research group achieved for the first time that a watt-scale solid-state Yb:CYA femtosecond laser frequency comb is fully locked to the carrier envelope phase shift frequency and repetition frequency, with a pulse width of 54 fs and an average power of 1.5 W. The free-running carrier-envelope offset (f_ceo) was observed with a signal-to-noise ratio of 40 dB at 100 kHz resolution bandwidth, and the residual phase jitter of the fceo after locking was only 370 mrad. When the duration is 3 hours and the counting gate time is 1 s, the standard deviation of f_ceo long-term frequency drift is only 0.8 mHz.In this paper, an all-solid-state Kerr lens mode-locked GHz femtosecond oscillator based on Yb:CYA crystal is introduced. A 980 nm fiber laser with a power of 8 W is used as the pump source, and the cavity type is a four-mirror ring cavity structure. In our experience the ring cavity has the advantages of stable mode locking, relatively insensitive to optical feedback, reducing the dispersion in the cavity and high repetition frequency compared with the linear cavity configuration. The transmission of the output coupler is 1.6%. The 3 mm Yb:CYA crystal is wrapped with indium foil and mounted in a copper block that is cooled by using a water cooler with temperature feedback to maintain a constant 13℃ temperature, and the sample is antireflection-coated for both the pump and laser wavelengths from 970 nm to 1 200 nm. The initiation of the mode locking is observed by a fast oscilloscope, and the oscillator is capable of generating GHz femtosecond pulses with a center wavelength of 1 051 nm and an average output power of 1.7 W with a pulse duration of 207 fs. The Radio Frequency(RF) spectra measurement shows that the fundamental frequency of the signal is about 1.02 GHz with a Resolution Bandwidth (RBW) of 100 kHz, spanning 5 MHz. The Signal-to-noise Ratios (SNR) is 50 dB, suggesting that the unidirectional KLM runs stably.To the best of our knowledge, this is the first time that an oscillator based on Yb:CYA crystal has achieved GHz repetition frequency watt-level femtosecond pulse output, which lays a solid foundation for further realization of high repetition frequency femtosecond optical frequency combs based on this oscillator.