A new computational scheme is developed to study gas accretion from a circumbinary disk .
The scheme decomposes the gas velocity into two components one of which denotes the Keplerian rotation and the other of which does the deviation from it .
This scheme enables us to solve the centrifugal balance of a gas disk against gravity with better accuracy , since the former inertia force cancels the gravity .
It is applied to circumbinary disk rotating around binary of which primary and secondary has mass ratio , 1.4:0.95 .
The gravity is reduced artificially softened only in small circular regions around the primary and secondary .
The radii are 7 % of the binary separation and much smaller than those in the previous grid based simulations .
7 Models are constructed to study dependence on the gas temperature and the initial inner radius of the disk .
The gas accretion shows both fast and slow time variations while the binary is assumed to have a circular orbit .
The time variation is due to oscillation of spiral arms in the circumbinary disk .
The masses of primary and secondary disks increase while oscillating appreciably .
The mass accretion rate tends to be higher for the primary disk although the secondary disk has a higher accretion rate in certain periods .
The primary disk is perturbed intensely by the impact of gas flow so that the outer part is removed .
The secondary disk is quiet in most of time on the contrary .
Both the primary and secondary disks have traveling spiral waves which transfer angular momentum within them .