Abstract: A readout chip based on the time over threshold technology was designed for silicon pixel detector used in high energy physics experiment. The chip was taped out with a 130 nm CMOS technology. There are 30×10 pixel units in one chip, and the size of one pixel unit is 50 μm×250 μm. Test results show that the equivalent input noise of the pixel unit circuit is less than 100e^- and the integral non-linearity is better than 4.2%. The basic functions are realized.