In order to improve the detection accuracy of all-fiber differential absorption lidar (DIAL), it is very important to develop configuration of all-fiber DIAL system with circulator at close range. Relationship between detection accuracy of DIAL and laser echo energy is analyzed. At close range, crosstalk of circulator affects the detection accuracy. The influence of crosstalk on detection accuracy is analyzed at different heights. Combined with the example of CO2 concentration detection and simulation, signal to noise rate (SNR) and relative error with height are analyzed. The research shows that crosstalk can interfere with laser echo and seriously affect detection SNR and accuracy. The study has important significance on the design and improvement of all-fiber DIAL system.