Effects of gap in primitive fir forest in southeast Tibet on species diversity of herb and shrub were studied. The results showed that species composition, distribution and diversity in gap were different from those in non-gap. The improvement of illumination and other habitat conditions resulted in richer species of herb and shrub in gap. There were shade-tolerant and photophilic herb species and shrub species in gap, however, only shade-tolerant herb species and shrub species grew in non-gap. Species diversity and evenness in gap were higher than in non-gap. The diminutive similar coefficient between herb and shrub communities showed that certain difference existed between herb and shrub communities in stands of gap and non-gap. The similar coefficients were little correlative between gap area and communities. Gap was important to improve growth of herb and shrub and maintain species diversity of primitive subalpine fir forest in southwest Tibet.