Aiming at the high accuracy measurement requirements of weak current signals, this paper proposes a circuit design scheme and software filter algorithm for fA level weak current measurement based on transimpedance measurement method. It focuses on the selection of key components, design of current-voltage conversion circuit, high-resolution AD conversion, noise identification and filtering, which realizes the high accuracy measurement of 2pA~200nA current. The test results indicate that the measurement resolution is up to 1 fA and the relative error is better than ± 1%.