In this paper, we study the following fractional Choquard equation (FC)(−Δ)su+V(x)u=(Iα∗|u|p)|u|p−2u,inRN,where s∈(0,1), N≥3, V(x) is continuous potential function, Iα:RN→R is the Riesz potential of order α defined by Iα(x)=|x|α−N for every x∈RN∖{0}, α∈(0,N), ∗ denotes the convolution operator, 2<p<N+αN−2s=2α,s∗, 2α,s∗ is the critical exponent in the sense of Hardy–Littlewood–Sobolev inequality and fractional Laplace operator and the operator (−Δ)s stands for the fractional Laplacian of order s. Combining constraint variational method, quantitative deformation lemma and the Brouwer degree theory, we prove that (FC) possesses one least energy sign-changing solution u0. Moreover, we show that the energy of u0 is strictly larger than 2p−2p−1 times and strictly less than four times the ground state energy.