Abstract: Poly α-olefin drag reducing agent (DRA) tends to suffer shear degradation in the process of its application. In this paper, the effects of the mass fraction of coupling agent KH550 and system temperature on the surface modification of nano-SiO₂ were investigated on the basis of the previous study on the polymer based nano-composite and nano-SiO₂/poly α-olefin DRA. Surface hydroxy number and oil adsorption value were used to characterize the test results and it is shown that modified nano-SiO₂ particles with less surface hydroxy and more oil adsorption are generated when the KH550 mass fraction is 15% and the system temperature is 50 ℃. The application performance of nano-DRA was tested by means of rotating disk and DRA loop test. It is revealed that the modified nano-SiO₂ particles can interact better with poly α-olefin to generate the composite DRA and the shear resistance of composite DRA is much better after it is sheared by the rotary disk and twice by the centrifugal pump. And it is indicated by the investigation on the modification conditions of nano-SiO₂ particles and the tests on drag reducing performance that composite nano-DRA is better on the performances of drag reduction and shear resistance than that of poly α-olefin DRA.