The present invention is the preparation process and apparatus for substituting alkyl group in high-carbon aluminium alkyl with ethylene to prepare straight-chain C4-26 alpha-olefine. High-carbon aluminum alkyl after being preheated to 120-180 deg.c is made to enter into a single-stage spraying tubular reactor at a linear speed of 150-300 m/s while ethylene after being preheated to 280-300 deg.c is made to enter into a reactor in tangent direction, so that replacement reaction is performed at 230-300 deg.c and 0.5-1.8 MPa. The atomizing reaction product is cooled to 20-60 deg.c and then, the emulsion is made to enter into the buffering tank in a double-disc separating tower for filming and separating while the gaseous phase is separated in the tower top for reuse. The coarse high-carbon alpha-olefine is fractionationed to obtain the destination product. |