Based on the social capital theory and the spiral of silence theory, this study suggested the process of SNS users’ public opinion expression on social issues. Based on the construal level theory, we examined how the opinion expression process specifically changes according to the individuals’ social distance. The motivational factors of willingness to speak out were presented as SNS social capital, current opinion congruency, and attitude certainty. SNS social capital positively affected current opinion congruency, attitude certainty, and willingness to speak out. Current opinion congruency did not significantly affect the willingness to speak out and positively influenced attitude certainty. Attitude certainty had a positive effect on the willingness to speak out. The social distance positively moderated the effects of SNS social capital on current opinion congruency, SNS social capital on attitude certainty. Also, the moderated mediating effect of social distance was found to be significant. This study proposed a new framework of the public opinion expression process that complements the spiral of silence theory through social capital theory. Moreover, this study detailed and concretely demonstrated the process of expressing opinions of SNS users from construal level theory.