The spin of the black hole is an important parameter which may be responsible for the properties of the inflow and outflow of the material surrounding a black hole .
Broad band IR/optical/UV spectrum of the quasar SDSS J094533.99+100950.1 is clearly disk-dominated , with the spectrum peaking up in the observed frequency range .
Therefore , disk fitting method usually used for Galactic black holes can be used in this object to determine the black hole spin .
We develop the numerical code for computing disk properties , including radius-dependent hardening factor , and we apply the ray-tracing method to incorporate all general relativity effects in light propagation .
We show that the simple multicolor disk model gives a good fit , without any other component required , and the disk extends down to the marginally stable orbit .
The best fit accretion rate is 0.13 , well below the Eddington limit , and the black hole spin is moderate , 0.3 .
The contour error for the fit combined with the constraints for the black hole mass and the disk inclination gives a constraint that the spin is lower than 0.8 .
We discuss the sources of possible systematic errors in the parameter determinations .