NOVELTY - A propane pre-cooling ethane-removing overhead reflux heavy hydrocarbon recovery process comprises propane pre-cooling cold tank unit, deethanization overhead reflux product liquid separating unit, natural gas liquid separating unit, natural gas heavy hydrocarbon unit, production device comprises propane evaporative cooling tank (1), 2 separators (7), 1 platform natural gas expander (8), multi-throttle valve (6), 1 contact tower (2), deethanizer (3), butane-removing tower (4), and mixer (20).    USE - Propane pre-cooling ethane-removing overhead reflux heavy hydrocarbon recovery process (claimed).    ADVANTAGE - The process greatly increases propane recovery rate and economic efficiency, fully uses propane pre-cooling unit, has compact and simple structure, is convenient to install and not sensitive to natural environment condition, reduces energy consumption, and does not need additional refrigerant.    DETAILED DESCRIPTION - A propane pre-cooling ethane-removing overhead reflux heavy hydrocarbon recovery process comprises propane pre-cooling cold tank unit, deethanization overhead reflux product liquid separating unit, natural gas liquid separating unit, natural gas heavy hydrocarbon unit, production device comprises propane evaporative cooling tank, 2 separators, 1 platform natural gas expander, multi-throttle valve, 1 contact tower, deethanizer, butane-removing tower, and mixer, and recovering natural gas from seabed is processed by preprocessing seabed to remove sand, water, acidic gas, mercury, benzene, and impurity which may propane pre-cooling cold tank unit, expanding propane evaporative cooling tank, pre-cooling natural gas using 3 level of refrigeration at 4.7 degrees C, - 15 degrees C, and - 36 degrees C in propane pre-cooling cold tank unit, separating gas phase from compressed propane by high pressure separator, medium pressure separator, and low pressure separator sequentially, cooling water, throttling liquid phase to recirculate in pre-cooling tank as cold source for cooling natural gas, liquefied petroleum gas (LPG), gas refrigerant, and deethanization overhead reflux product stream, feeding gas phase in deethanization overhead reflux product liquid separating unit to separate gas phase and gas phase product mixture, contacting gas phase with overhead gas phase product mixture, feeding in double contact expansion refrigerating liquefaction unit, separating liquid phase discharge and naturally cooled separating liquid phase mixture, recycling separating liquid phase mixture as contact material, feeding natural gas in pre-cooled gas-liquid separator to separate liquid phase, throttling liquid phase back to pre-cooling tank, feeding cooled gas expander in bottom of deethanization tower, expanding gas expander to 4.5 MPa in natural gas heavy hydrocarbon unit, separating using deethanization tower and butane-removing tower to remove natural gas hydrocarbon in which deethanizer overhead product is returned to pre-cooling tank, and butane-removing product is returned to LPG pre-cooling tank.    DESCRIPTION OF DRAWING(S) - The drawing shows a flow chart of liquefied process of propane pre-cooling ethane removing overhead reflux tower.    Propane evaporative cooling tank (1)    Contact tower (2)    Deethanizer (3)    Butane-removing tower (4)    Throttle valve (6)    Gas-liquid separator (7)    Platform natural gas expander (8)    Mixer (20)