There are many causes to make the vibration of reciproeating internal combustion-engine. The main causes are as follow: (1) no balanced reciprocating inertial force; (2) no balanced centrifugal inertia1 force; (3)twist changing in four processes; (4) press changing of gas in the cylinder. Because single cylinder internal-combustion-engine has no balance parts as multiple cylinder internal-combustion-engine, it is more clear in no balancing. The major affecting factors are no balanced reciprocating inertial force and centrifugal inertial foree. After analysing the no balanced inertial force of single cylinder internal-combustion-engine, the balanced equation were obtalned and several usual balancing methods were analysed. In these mainly analysing and discussing the over weight method is the simplest one. The results are about the balance weight in the opposite and leaning opposite direction to balance the first grade no balanced inertial force as well as about strongness and direction of the minimal force left no balanced. Otherwise, the problem of the first and the second grade inertial force is solved through data calculated mothod.