This paper analyzes the first secured four color light curves of V396 Mon using the 2003 version of the WD code .
It is confirmed that V396 Mon is a shallow W-type contact binary system with a mass ratio q = 2.554 ( \pm 0.004 ) and a degree of contact factor f = 18.9 \% ( \pm 1.2 \% ) .
A period investigation based on all available data shows that the period of the system includes a long-term decrease ( dP / dt = -8.57 \times { 10 ^ { -8 } } days/year ) and an oscillation ( A _ { 3 } = 0. ^ { d } 0160 ; T _ { 3 } = 42.4 years ) .
They are caused by angular momentum loss ( AML ) and light-time effect , respectively .
The suspect third body perhaps is a small M-type star ( about 0.31 solar mass ) .
Though some proofs show that this system has strong magnetic activity , through analyzing we found that the Applegate mechanism can not explain the periodic changes .
This binary is an especially important system according to Qian ’ s statistics of contact binaries as its mass ratio lies near the proposed pivot point about which the physical structure of contact binaries supposedly oscillate .