A new streak camera with more wider dynamic range and picosecond temporal resolution for soft X-ray was developed. The photocathode′s working area is 30 mm in diameter, and its focusing voltage is reduced to 8 kV to prevent electrical discharge. A post-accelaration system was introduced into the image tube for improving the phosphor screen′s quantum efficiency largely, and an external image intensifier with wide dynamic range was adopted. Experimental evaluation was carried out by means of a picosecond laser, and the results show that the dynamic range of more than 2000 can be achieved.