Let G = (V (G), E(G)) be a simple graph. A restrained double Roman dominating function (RDRD-function) of G is a function f : V (G) → {0, 1, 2, 3} satisfying the following properties: if f (v) = 0, then the vertex v has at least two neighbours assigned 2 under f or one neighbour u with f (u) = 3; and if f (v) = 1, then the vertex v must have one neighbor u with f (u) ≥ 2; the induced graph by vertices assigned 0 under f contains no isolated vertex. The weight of a RDRD-function f is the sum f (V ) = v∈V (G) f (v), and the minimum weight of a RDRD-function on G is the restrained double Roman domination number (RDRD-number) of G, denoted by γ rdR (G). In this paper, we first prove that the problem of computing RDRD-number is NP-hard even for chordal graphs. And then we study the impact of some graph operations, such as strong product, cardinal product and corona with a graph, on restrained double Roman domination number.