In　this　work,　an　in　situ　strategy　was　developed　to　construct　various　metal-carbon　heterostructures　with　high　yield.　Notably,　the　multi-step　reactions　and　structural　regulation　were　completed　in　milliseconds　due　to　the　greatly　enhanced　kinetic　driving　force　originated　from　the　ultra-high　temperature　and　ionized　reactive　atmosphere　in　thermal　plasma,　resulting　in　ultrasmall　metal　nanocrystals　with　size　about　several　nanometers　embedded　in　high-crystalline　and　nitrogen-doped　porous　carbon　nanolayer.　Based　on　controlled　experiments,　a　self-coordinated　mechanism　involved　the　catalytic　effect　of　metal　species　and　the　confined　growth　function　of　C　was　proposed　to　clarify　the　formation　of　heterogeneous　nanocomposites.　Furthermore,　the　advantage　of　synthesized　heterostructure　was　illustrated　by　its　superior　performance　of　electrocatalytic　hydrogen　evolution　from　water　splitting.　The　obtained　dual　CoNi@NC　presents　a　competitive　overpotential　of　149　mV　to　deliver　a　current　density　of　10　mA　cm-2,　together　with　98　%　preservation　of　initial　capacity　after　20　h　test,　highlighting　the　universality　of　this　work　to　construct　well-designed　metal/C　nanocomposites　with　potential　engineering　application　in　electrocatalytic　field.