This paper studied the changes, response mechanism and correlation of functional traits of Leymus chinensis during vegetative growth period under different levels of organic fertilizer, in an attempt to provide reference for the dynamic study of resources, environment and plant functional characters and the restoration of grassland ecosystem. The changing trend, difference, correlation and influence coefficient of functional characters of Leymus chinensis were analyzed by conic equation fitting, single factor multivariate analysis of variance, Pearson correlation analysis and integral (stepwise) regression. The results show that (1) Organic fertilizer could increase the leaf length, leaf area, natural leaf width, unfolded leaf width, specific leaf area, stem length, stem mass, and single plant mass of L. chinensis sativus from increasing at first and then decreasing. At the same time, the content of leaf dry matter and stem dry matter decreased. (2) Organic fertilizer could change the correlation among functional characters of Leymus chinensis, enhance the correlation between leaf area and specific leaf area, stem length and stem mass, and stem length and single plant mass, decrease the correlation between single leaf mass and single plant mass, leaf width and plant height. (3) Organic fertilizer could change the contribution rate of Leymus chinensis phenotypic traits (leave, stem, and plant height) to the single plant mass, and with the increase of fertilization level, the contribution rates of leave, stem and plant height tends to be balanced. The order of phenotypic traits affecting single plant mass of L. chinensis was leaf trait > plant height > stem trait. It was found that short-term application of organic fertilizer had a significant effect on the functional characters of Leymus chinensis, and the effect mainly occurred in the later stage of vegetative growth of Leymus chinensis, especially on the single plant mass. Among them, leaf length, unfolding leaf width, leaf area and plant height have great influence on the single plant mass of Leymus chinensis, while plant height is the most stable factor driving the change of single plant mass of Leymus chinensis. At the same time, the correlation between functional characters of Leymus chinensis was also affected by the level of fertilization. Fertilization not only enhanced the correlation of some functional traits, but also weakened the correlation among other traits, and there was a certain balance as a whole.