  We present a systematic analysis to determine and improve the pulsation
periods of 1637 known long-period Mira variables in M33 using $gri$-band light
curves spanning $\sim18$~years from several surveys, including M33 variability
survey, Panoramic Survey Telescope and Rapid Response System, Palomar Transient
Factory (PTF), intermediate PTF, and Zwicky Transient Facility. Based on these
collections of light curves, we found that optical band light curves that are
as complete as possible are crucial to determine the periods of distant Miras.
We demonstrated that the machine learning techniques can be used to classify
Miras into O-rich and C-rich based on the $(J-K_s)$ period--color plane.
Finally, We derived the distance modulus to M33 using O-rich Miras at maximum
light together with our improved periods as $24.67 \pm 0.06$~mag, which is in
good agreement with the recommended value given in the literature.
