Conventional　micro-lens　arrays　(MLAs)　for　a　light　field　imaging　system　can　capture　3D　images,　which　can　be　optically　reconstructed.　However,　the　sensed　images　frequently　suffer　from　a　fixed　or　limited　depth　of　field　(DOF)　of　MLAs.　In　this　work,　we　propose　composite　micro-lens　arrays　(CMLAs),　which　are　composed　of　electrically　tunable　liquid　crystal　MLAs　(LC　MLAs)　and　ultraviolet-curing　MLAs　(UVC　MLAs).　Moreover,　we　experimentally　confirmed　that　the　proposed　CMLAs　possess　a　tunable　and　improved　DOF　by　electrically　controlling　the　operating　voltages　applied　to　the　LC　MLAs　in　the　light　field　imaging　system.　In　the　single　LC　MLA,　the　focal　length　changes　from　1.62　mm　to　2.53　mm,　and　the　DOF　is　transferred　from　0.83　mm　to　23.85　mm　under　the　influence　of　the　operating　voltage.　The　focal　length　of　the　CMLAs　is　tunable　from　2.02　mm　to　3.68　mm　compared　with　LC　MLAs,　and　the　corresponding　DOF　could　vary　from　1.19　to　43.38　mm,　which　is　much　higher　than　that　of　the　single　LC　MLAs.　Furthermore,　the　CMLAs　can　capture　clear　images　at　large　depth　positions　under　lower　operating　voltages.　Therefore,　the　CMLAs　with　the　improved　and　adjustable　DOF　exhibit　potential　application　for　the　light　field　imaging　system　and　can　be　extended　to　the　industrial　and　medical　microscopy　applications.