We study the evolution of star-forming galaxies with 10(10)M(circle dot) < M-* < 10(11.6)M(circle dot) over the redshift range of 0.7 < z < 1.2 using the emission-line galaxies (ELGs) in the extended Baryon Oscillation Spectroscopic Survey (eBOSS). By applying the incomplete conditional stellar mass function (SMF) model proposed in Guo et al., we simultaneously constrain the sample completeness, the stellar-halo mass relation (SHMR), and the quenched galaxy fraction. We obtain the intrinsic SMFs for star-forming galaxies in the redshift bins of 0.7 < z < 0.8, 0.8 < z < 0.9, 0.9 < z < 1.0, and 1.0 < z < 1.2, as well as the SMF for all galaxies in the redshift bin of 0.7 < z <. 0.8. We find that the eBOSS ELG sample only selects about 1%-10% of the star-forming galaxy population at the different redshifts, with the lower redshift samples more complete. There is only weak evolution in the SHMR of the ELGs from z. =. 1.2 to z. =. 0.7, as well as the intrinsic galaxy SMFs. Our best-fitting models show that the central ELGs at these redshifts live in halos of mass M similar to 10(12)M(circle dot), while the satellite ELGs occupy slightly more massive halos of M similar to 10(12.6)M(circle dot). The average satellite fraction of the observed ELGs varies from 13% to 17%, with the galaxy bias increasing from 1.1 to 1.4 from z = 0.7 to 1.2.