The importance of goal clarity in college students' online self-directed learning cannot be overstated. Using micro-survey data from 1018 Chinese college students, this paper empirically investigates how goal clarity affects college students' perceived effectiveness of online self-directed learning using an ordered logit model. Subsequently, this paper constructed a mediation model of "goal clarity–self-monitoring-perceived learning effectiveness" to examine the mediating role of self-monitoring. In addition, we introduced the adoption of e-resources and analyzed their moderating effect on the relationship between goal clarity and perceived learning effectiveness. Finally, this study examined whether there are differences in the effects of goal clarity on the perceived learning effectiveness of different characteristic groups. The findings indicate that goal clarity significantly enhances college students' perceived learning effectiveness in Online Self-directed Learning, with self-monitoring as a mediator and e-resource adoption as a positive moderator in this relationship. Heterogeneity analysis revealed that goal clarity has a more pronounced promotional effect on online self-directed learning among college students from non-poor and good network conditions. Consequently, university education should foster college students' intrinsic motivation for learning, enhance academic monitoring and management, and bolster their level of e-resource adoption, thereby enhancing students' online learning effectiveness.