Abstract: In the measurement of ray intensity, the current signal from the integral ionization chamber is in the range of 10^-10~10^-15 A, which needs to be converted and amplified before it can be collected. A weak current signal amplification system is designed for the integral ionization chamber in this paper, using AC modulation technology to modulate the weak DC current signal to be measured into AC voltage signal, and then obtains the DC voltage signal after amplification, phase-sensitive detection, filtering and other circuit processing, and finally the data is collected. At the same time, the DC negative feedback is introduced into the system to shorten the response time of current measurement. The linear and response characteristics of the system were tested by the standard current source, and the β ray of tritium target was detected by an integral ionization chamber. The test results show that the system can effectively amplify the weak current signal in the range of 10^-14~10^-11 A with good linearity and response time characteristics, and the current measurement sensitivity is 10^-14 A, the system has a good prospect of engineering application.