When a solar flare, it radiates a lot of X-rays and high-energy particles, etc, and it makes large amounts of ionosphere substance ionized instantly, and, as the electron density of ionospheric change sharply, the equivalent reflection height of ionosphere changes too, thus causing the very low frequency signal's phase abnormal phenomenon. This paper conducts the phase abnormal situation of VLF signals, bases the date from VLF receiver in Xinxinag, Henan province, during the launch and return of “Shen zhou ???”, and then, conducts the data handling analysis of the abnormal phase with the least square method and gives out predicted flare level, and compares the results between VLF receiver's monitoring with the American GOES satellite, and the two results match exactly,thus verifying the feasibility of the method.