In order to improve the ablation quality of high fluence femtosecond laser， a Fabry-Perot cavity was used to generate femtosecond laser pulse trains whose pulse interval can be tuned continuously from 1 to 3 500 ps， and the ablation quality of silicon by single femtosecond pulses and pulse trains with different pulse intervals were systematically investigated. According to the experiment results， pulse trains with intervals around 50~100 ps achieved the most ideal ablation crater. The coronal redeposition materials at the edge of the crater were greatly reduced and the thickness reduced to 40% of that of single femtosecond pulses. In the meanwhile， there is almost no adhered dust or thermal damage on the surrounding substrate， and the quality factor increased from 0.52 to 0.89. The femtosecond laser pulse trains reported in this paper， on account of the interaction of subsequent pulses and ejected material， when the pulse interval is in the range of 50~100 ps， the subsequent pulses of which can fully atomize the ejected material， thus reduce the coronal redeposition materials and contamination and damage of high-temperature dust and improve the ablation quality.