Understanding the electronic anisotropic state at a temperature associated with the nematic phase is unresolved problems in iron pnictides. Although many experiments focus on electron nematic phase, the origin of such nematic phase is still debated. Theoretical proposals explored two scenarios for nematic order, spin or orbital. No matter which one is the driving force, that could induce the strucural transition and magnetic transition. Considered that the structural transition is a second order in BaFe2As2 but a first order in SrFe2As2. Our recent time-of-flight neutron scattering experiments on detwinned BaFe2As2 and SrFe2As2 have been successful carried out, and reveal that the spin nematiciy of SrFe2As2 ceases at Ts, but for BaFe2As2 ceased above Ts. It will be interesting to explore the spin nematicity in Ba0.9Sr0.1Fe2As2,which on the critical point of first order and second order.