Investigations on density limit have been performed under a variety of discharge conditions on HL-1M, which include hydrogen isotope, siliconized wall coating and a variety of fuelling methods (gas puff, pellet and supersonic molecular beam (SMB) injection). Detailed analysis shows that the HL-1M density limit is a disruptive limit and related to first wall recirculating and fuelling methods. The destruction of the balance between radiation and input power is the main reason for the density disruption.