The nonlacalized interference in multiple-beam interferometer was studied. The reflex light intensity distribution function was obtained. The numerical analysis shows that as the reflection coefficient of specular surface increase, the stripe of the nonlocalized interference becomes sharp, resolution ratio is improved, while the half-value width decreases; narrow bright stripe nearby the dark stripe exists at low interference order with higher reflection coefficient of specular surface; the amplitude of the bright stripe gradually decreases to the background intensity; the oscillation becomes more obviously at lower interference order; the first reflex light provides an uniformity background, and the second reflex light makes a double beam interferes with the first reflex light; with the introduce of more reflex lights, the dark stripe becomes sharp and many low intensity interference stripes appear between neighbour dark stripes; the low intensity interference stripes between the dark stripes disappear and narrow bright stripes nearby the dark stripes arise while with sufficient reflection lights. At last, the filter based on the multiple beam nonlocalized interference theory was investigated. The filtering bandwidth of the nonlocalized interferometer can be reduced notably by increasing the reflection coefficient of specular surface. While changing the mirror spacing, the filtering wavelength and the interval can be adjusted flexibly.