The short-term frequency instability of the solid-state laser was measured by using the self-beat of fiber-delay method. The Tm, HoYLF microchip laser which was cooled by liquid nitrogen provided with single longitudinal-mode, narrow linewidth output and the power was up to milliwatt. In experiment, at the fixed fiber length of 500 m, self-beat signals of the laser under the integral time about 2ms, 4ms, 40ms, 100ms were obtained. And under different fiber lengths about 100 m, 200 m, 300 m, 400 m, 500 m, the corresponding time delay is 0.5 μs, 1 μs, 1.5 μs, 2 μs, 2.5 μs, and the self-beat signal of the laser was achieved. The short-term frequency instability of Tm, HoYLF microchip laser is 1.48 kHz/μs. Meanwhile the relationship between laser frequency stability and laser linewidth is discussed.