Solar flares are the most violent outbursts that occur in localized regions of the solar atmosphere. They emit large amounts of X-rays and energetic particles. X-rays reaching the earth at the speed of light will disrupt the calm ionospheric environment, causing sudden ionospheric disturbance (SID), which will make the very low frequency (VLF) signal to sudden phase anomaly (SPA), lead to the positioning error of satellite navigation system and interfere with satellite communication. Energetic particles will arrive near the satellite orbit in 1-3 days, causing direct damage to the satellite. They may also cause geomagnetic storms after reaching the Earth. In this paper, we mainly study to monitor solar activity and calculate solar flare class through the phase variation of VLF signal by combining the theory of VLF waveguide mode in order to forecast the environment of satellite navigation and communication. In addition, it can also predict the energetic particles and geomagnetic storms 1-3 days in advance according to the time and class of flare outbreak, so that the protective measures for satellite to operate safely could be taken in advance.