An undulator consists of many magnets. The unavoidable remanence divergence and dimension divergence of these magnets cause the undulator magnetic field error

including the peak magnetic field error

phase error

etc

which will affect the quality of the spontaneous emission spectrum. This paper presents the simulation method of permanent magnet magnetic field

undulator magnetic field and spontaneous emission. The normal school random numbers generator is applied to produce groups of magnets of different remanences or different sizes. Each group of the magnets can constitute the undulator. Then the spontaneous emission is calculated. And accordingly we can make a study of the influence of undulator magnetic field errors on spontaneous emission. Finally

the correlations between intensities of spontaneous emission and various magnetic filed errors are illustrated

including RMS magnetic remanence error

RMS magnetic width error

RMS phase error and RMS field error.