文章结合理论分析与经验分析，探究了高等教育机会的家庭出身差异及其时间变化趋势。理论分析部分，文章构建了一个简单的理论模型，推导出高等教育机会的获得存在家庭出身差异，家庭出身较好的个体更易获得高等教育机会，但这一差异会随着高等教育扩张而缩小。经验分析部分，文章使用CGSS2008-2017年度数据，进行了描述分析与回归分析。使用“辈出率”指标进行描述分析后发现：高等教育机会的获得存在明显的家庭出身差异，且这一差异在父母受教育程度上的表现最为突出。家庭出身为14岁时家庭经济地位处于社会中上层、父母受教育程度在大专及以上、14岁时父母在党政机关工作的个体，最有可能获得高等教育机会。认为自己14岁时家庭经济地位处在社会顶层的个体获得高等教育机会的概率并非最高反倒是最低。整体而言，从60后到90后，高等教育机会获得的家庭出身差距变小了。使用logit模型进行回归，估计结果与描述分析关于家庭出身差异的结论一致，另外，家庭经济地位对个体高等教育机会获得的边际效应呈现出明显的“先上升，后下降”的趋势。在logit模型中引入家庭出身与出生年代相乘的交互项，结果显示，1980年之后出生的个体的高等教育机会获得存在一个“梳子效应”，即家庭出身差距变得越来越小。这把“无形的梳子”很可能是高校扩招政策。

Combining theoretical analysis and empirical analysis, this paper probes into the family origin differences in higher education opportunities and its time trend. In the theoretical analysis part, this paper constructs a simple theoretical model and deduces that there are family background differences in obtaining higher education opportunities. Individuals with better family background are more likely to obtain higher education opportunities, but this difference will shrink with the expansion of higher education. In the empirical analysis part, this paper uses CGSS2008-2017 data to conduct descriptive analysis and regression analysis. After the index of "seniority rate" is used to describe and analyze, it is found that the access to higher education opportunities has obvious family background differences, and this difference is most prominent in the educational level of parents. Individuals from families with an upper-middle economic status at age 14, parents with a college degree or above, and parents working for the party or government at age 14 are most likely to have access to higher education. Individuals who rated themselves at the top of the economic ladder at age 14 are not the most likely to have access to higher education, but the least likely. Overall, from the post-60s generation to the post-90s generation, the family origin gap in access to higher education narrowed. logit model was used for regression, and the estimated results were consistent with the conclusion of the description analysis on the difference of family birth. In addition, the marginal effect of family economic status on the access to higher education opportunities of individuals showed an obvious trend of "up and down". By adding the interaction term multiplied by family birth and birth years into the logit model, the results show that there is a "comb effect" in the access to higher education opportunities of individuals born after 1980, that is, the gap between family birth becomes smaller and smaller. This "invisible comb" is likely to be the university enrollment expansion policy.