  We study the evolution of star-forming galaxies with $10^{10}
M_\odot<M_*<10^{11.6} M_\odot$ 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
(ICSMF) 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 stellar mass functions 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 stellar mass function 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 to be 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 stellar mass
functions for lower-mass galaxies of $M_*<10^{11} M_\odot$. There is
significant decrease of the stellar mass function for star-forming galaxies
with redshift at the massive end. Our best-fitting models show that the central
ELGs at these redshifts live in halos of mass $M\sim10^{12} M_\odot$ while the
satellite ELGs occupy slightly more massive halos of $M\sim10^{12.6} M_\odot$.
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.
