Abstract: Image-converter tube streak cameras are commonly used in study on ultra-high speed physical phenomena.The sweep speed and its nonlinearity are main parameters of an image-converter tube streak camera and its accuracy has great effect on experimental results of ultra-high speed physical phenomena.The cause of nonlinearity was explained in theory.A method was introduced to calibrate the sweep speed and its nonlinearity,in which a picosecond light pulse source,an etalon and a high precision time delay device was used.Better experimental results were obtained with ±3.52% maximum nonlinearity of the sweep speed and its relative error of measurement was ±1.4%,which improved the reliability of experimental data processing and analysis effectively.