Brand position overlap is a common phenomenon in real business world.Based on the theory of ecology,a set of quantitative method was put forward to assess the status of brand position.In the first part of the paper,a brief introduction about the concept of niche as well as how to measure it was made.Then the paper presents a new concept of brand niche and indexes of it:brand niche breadth and brand overlap.With a review of the existing methods of niche,a formula of brand niche breadth was given based on a symmetrica method and brand niche overlap theory was used to describe the competition of brands in market environment.Finally,the method of measuring brand breadth was applied to five major Chinese internet portal brands,and the results show that the assessment approximates to reality.