1. An automatic placement system of IC design, comprising: an input module, for receiving component data and setting parameters, the setting parameters including a crossover rate, a mutation rate and a termination condition; a processing module, for executing a genetic algorithm according to the setting parameter to randomly generate a plurality of populations, the populations being a plurality of zeroth-generation chromosome sequences, computing a plurality of computing values of each of the chromosome sequences according to the component data, computing a fitness value of each chromosome sequence from the computed computing values of each chromosome sequence, evolving the chromosome sequence into a next generation genetic evolution repeatedly, selecting some of the chromosome sequences according to the fitness value of each chromosome sequence, determining whether or not to perform a crossover of the selected chromosome sequence according to the crossover rate to produce a plurality of sub-generation chromosome sequences, determining whether or not to perform a mutation of each sub-generation chromosome sequence according to the mutation rate, each of the sub-generation chromosome sequences and the chromosome sequence of a previous generation jointly constituting a next generation population, and the genetic evolution being executed repeatedly until the termination condition is satisfied, and the processing module selecting the best chromosome sequence from the chromosome sequences according to the fitness value of each chromosome sequence of the population of each generation, and the computing values including a positive and negative isotype rate which is equal to (Number of placement components−Number of positive and negative switches)/(Number of placement components); and an output module, for outputting a best placement method according to the best chromosome sequence.