The mechanism of reproducing more viable offspring in response to selection is considered as a major factor influencing the advantages of sex. In diploids, sexual reproduction combines genotype by recombination and segregation. Theoretical studies of sexual reproduction have investigated the advantage of recombination in haploids. However, the potential advantage of segregation in diploids is less studied. The present study aimed to quantify the relative contribution of recombination and segregation to the evolution of sex in finite diploids by using multi-locus simulations. The model calculated the mean fitness of a sexually or asexually reproduced offspring to describe the long-term effects of sex. The evolutionary fate of a sex or recombination modifier was also monitored to investigate the short-term effects of sex. We considered two different scenarios of mutations in finite populations to investigate the evolution of a sex or recombination modifier: (1) only deleterious mutations were present and (2) a combination of deleterious and beneficial mutations. Results showed that the combined segregation and recombination strongly contributed to the evolution of sex in diploids. If deleterious mutations were only present, segregation efficiently slowed down the speed of Muller's ratchet. As the recombination level was increased, the accumulation of deleterious mutations was totally inhibited and substantially contributed to the evolution of sex. The presence of beneficial mutations evidently increased the fixation rate of a recombination modifier. We also observed that the twofold cost of sex was easily to overcome in diploids if a sex modifier caused a moderate frequency of sex.