Laser spike of soft X-ray pumped by capillary discharge is measured at 25 Pa pressure and 27 ns rise time of the current pulse with X-ray diode (XRD) coated with a gold layer. The characteristic of this laser is studied. The low pressure and the short rise time of the current pulse lead to a fast compression of the plasma. In this condition, the laser spike with the duration of 1.6 ns near the peak of the ground light is obtained. The angle of divergence and gain coefficient of the spike at fast Z-pinch are measured. The angle of divergence measured by shifting the pinhole is 5.3 mrad. By changing the length of gain medium, the gain coefficient is measured as 0.45 cm-1 and gain-length product as 8.28. In addition, a monochromator is used and the laser spike about 46.9 nm is observed.