K2CO3 was utilized as an friendly catalyst for the environmentally fast and simple synthesis of ten 3-substituted coumarin derivatives by the Knoevenagel condensation of salicylaldehyde and its derivatives with diethyl malonate, ethyl acetoaceate or methyl acetoaceate under solvent free conditions. Three effect on the yield of coumarin-3-ethyl formate was investigated. The results showed that coumarin-3-ethyl formate were obtained 88.1% yields within based on 20 mmol of salicylaldehyde, molar ratio of salicylaldehyde to diethyl malonate 1：1.2, dosage of K2CO3 0.1 mmol and time of reaction 15-18 min. When ethyl （or methyl） acetoaceate displaces diethyl malonate, 3-acetyl coumarin were synthesized with the yield 84.7%（or 82.9%）. When solid substituted salicylaldehyde displaces salicylaldehyde with diethyl malonate, ethyl （or methyl） acetoacetate at a mole ratio of 1：2.0, eight 3-substituted coumarin derivatives were synthesized with the yield from 62.5%-89.0%（or 58.1%-83.0%）.