The accuracy of the present flow analyzer method for determination of low content of effective phosphorus extracted from sodium bicarbonate was not good，and it was difficult to be used for batch samples detection and analysis. Therefore，an improved method was proposed. The results were compared with the present method and artificial colorimetric method，and the feasibility of determination of soil effective phosphorus by the improved method was discussed. The results showed that the results of the present method，artificial colorimetric method and improved method for the determination of effective phosphorus in the range of 0.60～1 mg/L tended to be consistent，and there was no significant difference(P>0.05). When the effective phosphorus content of the samples with 0.04～0.60 mg/L was determined by the present method，artificial colorimetric method and improved method，and the results of the present method were significantly different from those of the other two methods(P<0.05)，while there was no significant difference between the results of the artificial colorimetric method and the improved method(P>0.05). The regression equation of effective phosphorus content measured by artificial colorimetric method and current method was Y(artificial colorimetric method)=0.759X(present method)+0.166(R2=0.811 P<0.01). There was a significant correlation between effective phosphorus content measured by two methods. The regression equation of effective phosphorus content measured by artificial colorimetric method and improved method was Y(artificial colorimetric method)= 0.894X(improved method)+0.024(R2 =0.973 P<0.01)，and the effective phosphorus content measured by two methods showed an extremely significant correlation. Comprehensive comparison showed that the improved method was superior to the present method. The pipe setting of the present method determined that the carbon dioxide gas generated by the reaction between sodium bicarbonate and acid would affect the regularity and stability of the pipe bubble，resulting in the fluctuation of baseline，and the accuracy of samples with low effective phosphorus content would decrease. The pipeline settings of the improved method were optimized，carbon dioxide gas was eliminated online，interference was eliminated，the regularity of pipeline bubbles was guaranteed，and the baseline was stable，the relative standard deviation of the determination of low content effective phosphorus was less than 8.90%，and the recovery was between 94%～106%. The detection accuracy and precision were good. The improved method could be recommended for the detection and analysis of batch soil samples with different contents of effective phosphorus.