Features of L-H transition are investigated using the supersonic molecular beam injection (SMBI) with directional velocity under low heating powers in the present paper. Comparing the edge density profiles, it is analyzed that the conventional gas puffing (GP) and SMBI have effects on L-H transition. Experimental results suggest that the SMBI does directly trigger L-H transition on HL-2A, and it considerably reduces the power threshold of L-H transition. After abundant experimental data are analyzed and processed, it is found that the minimum L-H transition power with SMBI decreases by 10% when it is compared with GP trigged H-mode under same conditions.