In this paper, we are concerned with the anti-symmetric solutions to the following elliptic system involving fractional Laplacian {(−Δ)su(x)=um1(x)vn1(x),u(x)≥0,x∈R+n,(−Δ)sv(x)=um2(x)vn2(x),v(x)≥0,x∈R+n,u(x′,−xn)=−u(x′,xn),x=(x′,xn)∈Rn,v(x′,−xn)=−v(x′,xn),x=(x′,xn)∈Rn, where 0<s<1, mi,ni>0(i=1,2),n>2s,R+n={(x′,xn)|xn>0}. We first show that the solutions only depend on xn variable by the method of moving planes. Moreover, we can obtain the monotonicity of solutions with respect to xn variable (for the critical and subcritical cases mi+ni≤n+2sn−2s(i=1,2) in the L2s space). Furthermore, when m1=n2=p,n1=m2=q, in the cases p+q+2s≥1, we obtain a Liouville theorem for the cases p+q≤n+2sn−2s in the L2s space. Then, through the doubling lemma, we obtain the singularity estimates of the positive solutions on a bounded domain Ω. Using the anti-symmetric property of the solutions, one can extend the space from L2s to L2s+1, we can still prove the Liouville theorem in the extended space. With the extension, we prove the existence of nontrivial solutions.