The invention provides an application of organosilane, a polyolefin in-kettle alloy and a preparation method thereof. The preparation method for the polyolefin in-kettle alloy comprises the following steps: enabling a first olefin monomer to carry out first polymerization reaction in the presence of a catalyst; introducing a second olefin monomer into a polymerization reaction system to carry out second polymerization reaction, wherein the first olefin monomer is different from the second olefin monomer; first polymerization reaction and/or second polymerization reaction is carried out in the presence of organosilane with a general formula of R1mSiXn(OR2)k; R1 is C2-C20 alkyl and a R1 terminal comprises alpha-olefin double bonds, a norborneol alkenyl group, a cycloolefin group or a dicyclopentadiene group; X is halogen; R2 is a C1-C20 linear chain, a branched chain or isomerized alkyl; m is an integer number from 1 to 3; n is an integer number from 1 to 3; k is an integer number from 0 to 2; and m+n+k is equal to 4. Cross-linking degree of a rubber phase in the polyolefin in-kettle alloy obtained from the preparation method is relatively high, and the polyolefin in-kettle alloy has relatively high toughness and relatively low tensile breaking strength.