Picosecond diagnostics system is used to provide parameters of laser facility and help it to achieve designed technical aim. This system will diagnose parameters of compressed pulse for petawatt laser such as energy, pulse width, farfield, and pulse contrast. Root-mean-square (RMS) error is adopted to describe stability of diagnostics system in order to test its performance. Energy measurement range is 10~1000 J, RMS error of calibration data is 2.2%. Pulse width measurement range is 0.5~18.0 ps, temporal resolution is 0.07 ps for Gaussian type pulse, and data RMS error is 3%. Farfield measurement range is 150 diffraction limitation (DL), spatial resolution is 0.3 DL, and RMS error is 0.15%. Pulse contrast measurement range is 30 ps, temporal resolution is 0.3 ps, and dynamic range is 106. In experiments on petawatt laser, picosecond diagnostics system provides these parameters instantaneously and successfully to analyze petawatt laser facility′s performance.