The labor behavior in internal labor market is the behavior of both economic cooperation and social reciprocation . The pure economic yield and cost analysis of this behavior will deprive it of its social behavior characteristics . But emotional exchange theory provides a suitable perspective and analytic framework . The article studies internal labor market by applying the economic-sociological theory in terms of reciprocal social behavior in small groups . Factors such as information and market change lead to efficiency problems of labor management in firms . To clearly define labor boundary is not a low-cost or high-efficiency choice . Firms thus are forced to apply ambiguous boundary to internal labor division . With a certain degree,the ambiguous boundary of internal labor division helps to reduce the labor management cost and promote the autonomous reciprocal behavior among the internal workers (namely by way of exchanging labor skills,knowledge,information and others between the internal workers) . In the situation of applying ambiguous boundary to labor division,reciprocal social behavior in small groups of internal workers helps to reduce transaction cost,promote labor harmony,and thus enhance labor efficiency . The reciprocal behavior leads to the spillover of higher-skilled workers's kills and their economic yield externalization . And the economic externality of the spillover of higher-skilled workers'skills is not compensated by economic yield in labor pricing,but by emotional yieldin cooperative reciprocal behavior .The reciprocal behavior enhances the marginal labor productivity of lower-skilled workers and thus increases their labor yield . Therefore,the externalization contributes toformthe dual-structureof labor market,namely,the relative shortage of higher-skilledworkers caused by their relatively lower wage than average,and the relative surplus of lower-skilled workers due to their relatively higher wage . However,the externalization of the spillover of higher-skilled workers'skills can be compensated by social appreciation and respect for them,which increases the total labor yield by internalizing this emotional yield . The internalization of the emotional yield may help cope with the shortage of higher-skilled workers in labor market . The limit of this article is that it lacks of theoretical modeling and empirical data,which will be included in follow-up studies .