Fu Xian Sheng Bie Zhui Le, Da Xiao Jie Shi Jia De

Fu Jing Yan rescues a girl who eerily resembles his sister. Unfortunately, she appears to be mentally challenged. Nonetheless, he is determined to use her to thwart his bastard half-brother and his father while taking emotional solace in her resemblance to his beloved sister.
Meanwhile, Si Nian hides behind the roles she is playing for him and his family and takes the opportunity to get revenge on the prominent family that abused and then casually discarded her.
But when she is found out, their relationship becomes more entangled, not less.
(Source: LadyDragon at MDL)