The discovery of pressure induced superconductivity in non-collinear helimagnet CrAs has generated great interest in understanding its microscopic magnetic properties and their relationship to superconductivity. Our recent neutron diffraction experiment on CrAs has shown that it exhibits a spin reorientation from ab to ac plane along with an abrupt drop of the propagation vector under a critical pressure (Pc~0.6 GPa), where bulk superconductivity emerges. And the Cr moments between nearest neighbors tend to be aligned antiparallel with increasing pressure toward the optimal superconducting regime, suggesting that antiferromagnetic interactions are essential for superconductivity. Therefore, investigation of the spin excitations in the parent compound should give quantitative insight into the relationship between magnetic exchange interactions and superconductivity in this system.