In this paper, we investigate the following fractional Sobolev critical Nonlinear Schrödinger coupled systems: $$\begin{aligned} \left\{ \begin{array}{lll} (-\Delta )^{s} u=\mu _{1} u+|u|^{2^{*}_{s}-2}u+\eta _{1}|u|^{p-2}u+\gamma \alpha |u|^{\alpha -2}u|v|^{\beta } ~ \text {in}~ {\mathbb {R}}^{N},\\ (-\Delta )^{s} v=\mu _{2} v+|v|^{2^{*}_{s}-2}v+\eta _{2}|v|^{q-2}v+\gamma \beta |u|^{\alpha }|v|^{\beta -2}v ~~\text {in}~ {\mathbb {R}}^{N},\\ \Vert u\Vert ^{2}_{L^{2}}=m_{1}^{2} ~\text {and}~ \Vert v\Vert ^{2}_{L^{2}}=m_{2}^{2}, \end{array}\right. \end{aligned}$$
(
-
Δ
)
s
u
=
μ
1
u
+
|
u
|
2
s
∗
-
2
u
+
η
1
|
u
|
p
-
2
u
+
γ
α
|
u
|
α
-
2
u
|
v
|
β
in
R
N
,
(
-
Δ
)
s
v
=
μ
2
v
+
|
v
|
2
s
∗
-
2
v
+
η
2
|
v
|
q
-
2
v
+
γ
β
|
u
|
α
|
v
|
β
-
2
v
in
R
N
,
‖
u
‖
L
2
2
=
m
1
2
and
‖
v
‖
L
2
2
=
m
2
2
,
where $$(-\Delta )^{s}$$
(
-
Δ
)
s
is the fractional Laplacian, $$N>2s$$
N
>
2
s
, $$s\in (0,1)$$
s
∈
(
0
,
1
)
, $$\mu _{1}, \mu _{2}\in {\mathbb {R}}$$
μ
1
,
μ
2
∈
R
are unknown constants, which will appear as Lagrange multipliers, $$2^{*}_{s}$$
2
s
∗
is the fractional Sobolev critical index, $$\eta _{1}, \eta _{2}, \gamma , m_{1}, m_{2}>0$$
η
1
,
η
2
,
γ
,
m
1
,
m
2
>
0
, $$\alpha>1, \beta >1$$
α
>
1
,
β
>
1
, $$p, q, \alpha +\beta \in (2+4s/N,2^{*}_{s}]$$
p
,
q
,
α
+
β
∈
(
2
+
4
s
/
N
,
2
s
∗
]
. Firstly, if $$p, q, \alpha +\beta <2^{*}_{s}$$
p
,
q
,
α
+
β
<
2
s
∗
, we obtain the existence of positive normalized solution when $$\gamma $$
γ
is big enough. Secondly, if $$p=q=\alpha +\beta =2^{*}_{s}$$
p
=
q
=
α
+
β
=
2
s
∗
, we show that nonexistence of positive normalized solution. The main ideas and methods of this paper are scaling transformation, classification discussion and concentration-compactness principle.