In order to make full use of the advantages of flow analyzer，and accurately and efficiently determine the total nitrogen and total phosphorus content of plants at the same time，the existing method was improved，and the improved method was compared and analyzed with that of the traditional method.The feasibility of improving the method for simultaneous determination of total nitrogen and total phosphorus in plants by flow analyzer was discussed.The results showed that there was no significant difference of total nitrogen content by improved method and the diffusion method(P>0.05)，and there was no significant difference of total phosphorus by improved method and the molybdenum-antimony colorimetric method(P>0.05).The regression equation of improved method and diffusion method to determine the total nitrogen content was:Y(diffusion method-N)=0.978X(flow analyzer-N)+0.502(r2=0.9755，P<0.01)，the total nitrogen measured by the two methods was extremely significant correlation.The regression equation of improved method and molybdenum-antimony colorimetric method to determine the total phosphorus content was:Y(molybdenum-antimony colorimetric method-P)=0.985 X(flow analyzer-P)+ 0.035(r2=0.9835，P<0.01)，the total phosphorus measured by the two methods was extremdy significant correlation.The improved methods for determing the total nitrogen and total phosphorus content of plants with a flow analyzer had standard addtion recovery rates of 98.23%～100.68% and 98.67%～99.11% ，respectively.The relative standard deviation of the total nitrogen and total phosphorus content of three samples were repeatedly measured for four times were less than 6%.The improved method of simultaneous determination of total nitrogen and total phosphorus by flow analyzer had the advantages of simple operation，high precision and accuracy，less reagent consumption and high detection efficiency，which was suitable for the detection and analysis of large quantities of plants.