The effects of microbial agent application amount and alginic acid application concentration on the photosynthesis and root growth of Astragalus membranaceus were explored to provide theoretical reference for the ecological planting of Astragalus membranaceus with reasonable fertilization. A two-factor split zone pot experiment was adopted，and Astragalus membranaceus seedlings were used as materials. The application amount of microbial agent（M0：0 g/m² ，M1：3 g/m² and M2：6 g/m² ）was the main factor，and the application concentration of alginic acid（A0：water control，A1：4 g/L and A2：8 g/L）was the secondary factor，and the relevant indicators of Astragalus membranaceus leaves，rhizosphere soil，and roots were measured. The results showed that with the increase of microbial agent application amount，the photosynthesis of leaves，microbial content and enzyme activity in rhizosphere soil，endogenous hormone content in roots， roots dry matter accumulation and agronomic traits，and the medicinal components content in the roots were increased by 4.6% to 41.2%，10.1% to 27.7%，10.7% to 18.7%，6.9% to 16.9% and 23.1% to 29.9%，respectively. With the increase of alginic acid application concentration，the above indicators of Astragalus membranaceus showed a trend of first increasing and then decreasing. The improvement of photosynthesis，rhizosphere soil microbial content and enzyme activity， endogenous hormone content，and agronomic traits was conducive to the improvement of yield and quality. Microbial agent and alginic acid of appropriate concentration could enhance the photosynthesis of Astragalus membranaceus leaves，increase the microbial content and enzyme activity in the rhizosphere soil，promote root growth and development，and improve the yield and quality of Astragalus membranaceus. M2A1 treatment（microbial agent application amount of 6 g/m² ，alginic acid application concentration of 4 g/L）had the best effect. Under this treatment，the roots dry matter accumulation was 10.55 g/plant，the astragaloside IV content was 0.159%，and calycosin-7-glucoside content was 0.055%. This could provide theoretical reference for ecological planting of Astragalus membranaceus with rational fertilization in large fields.