In recent years,many couples in rural areas have decided to give up the additional births though they are allowed to do so by the birth control policy.To probe much more new variable factors in sound progress of population development in the future,this paper proposes to take Liping County of Guizhou Province as an example on how they give up the right of legally having the second child for empirical analysis through documentary study,questionnaires,home interviews and group discussion.We systematically analyzed the drivers,development trend,positive and negative effects and countermeasures for this phenomenon.The analysis results indicate that the following are the main drivers:concept change of the marriage,a stimulus of the interest-oriented policy,economic constraints and satisfaction of the preference for boys.In addition to those,the pension insurance,emergency risk,the cultural tradition and community public opinion are other factors to hinder the further development of this phenomenon.Meanwhile,with increasing families of putting off and abandoning the second childs birth,the phenomenon can not only bring the positive effects such as decreasing the speed of population growth,soothing social pressure,raising the peoples living standard and quality etc.,but also bring negative effects such as unbalanced higher birth gender ratio,weakened family function,birth energy backlogging and the problem of population ageing etc.In order to promote the sound development of the phenomenon,we have to build up a good social environment and carry on the system construction and so on.The analysis finally shows that the complicated forces and multidimensional effects of the phenomenon in Liping county of Guizhou Province proves the special condition causes and route trend of abandoning the "legal second child birth" in western ethnic poverty-stricken areas.The possible demographic affects should be highlighted by central government and responded from multiple angles.