Method and system for acquiring magnetic declination based on longitude and latitude

The invention provides a method and a system for acquiring a magnetic declination based on longitude and latitude, and the method and the system are used for acquiring the numerical value of a related magnetic declination by performing related conversion model calculation according to related numerical values after acquiring the longitude and latitude in geological acquisition work in a mobile field. The method mainly comprises the steps of obtaining a spherical harmonic Gaussian coefficient of a basic epoch by downloading a WMM.COF file and analyzing the file, constructing an earth magnetic field model through a Gaussian spherical harmonic function and the spherical harmonic Gaussian coefficient so as to obtain a magnetic declination corresponding to each order of spherical harmonic function, and obtaining a magnetic declination corresponding to each order of spherical harmonic function by using the earth magnetic field model and a spherical trigonometric algorithm. The geologically acquired longitude and la