In-tube　solid　phase　microextraction　(IT-SPME)　utilizing　molecularly　imprinted　polymers　(MIPs)　as　extraction　phase　has　received　wide　attention　due　to　various　merits.　However,　low　extraction　efficiency　and　unsatisfactory　recognition　performance　have　limited　its　extensive　application.　To　circumvent　the　limitations,　a　new　strategy　that　implementation　of　magnetic　fields　during　extraction　stage　was　introduced　to　improve　the　extraction　efficiency　and　recognition　performance　of　MIPs-based　IT-SPME.　Firstly,　using　2,4-dinitroaniline　(2,4-DNA)　as　model　template,　a　MIP　mingled　with　magnetic　nanoparticles　(Fe3O4)　was　in-situ　prepared　in　a　capillary　and　employed　as　the　microextraction　column　of　IT-SPME.　In　the　second　step,　a　magnetic　coil　was　wrapped　the　as-prepared　MIPbased　microextraction　column　so　as　to　produce　variable　magnetic　fields　in　extraction　step.　Results　revealed　that　the　application　of　magnetic　field　during　the　adsorption　step　improved　the　specific　extraction　performance　towards　template.　The　extraction　efficiency　and　imprinting　factor　towards　2,4-DNA　increased　from　58%　and　2.5　to　81%　and　3.1,　respectively.　Practicality　of　the　introduced　magnetism-assisted　IT-SPME　technique　based　on　MIP　was　demonstrated　by　on-line　hyphenating　with　HPLC/DAD　to　quantify　trace　2,4-DNA　in　a　variety　of　environmental　waters.　High　sensitivity　(limit　of　detection　was　0.060　mu　g/L),　good　precision　(RSDs　were　below　10%)　and　satisfactory　recoveries　(82.1-111%)　were　obtained.　Furthermore,　the　possible　selective　extraction　mechanism　under　magnetic　fields　was　deduced.