DNA computer is a new research field which combines both the computer science and molecular biology. DNA computer is proposed to solve a class of hard problems of mathematical complexity by using a set of DNA sequences encoding all candidate solutions to the computational problem of interest and find out the correct answers by serial manipulations of biochemical reactions. DNA computer is exactly a biomolecular computer which stores a vast quantity of information with high density. DNA computer, by means of its huge parallel computation and brute force search strategy, can solve the NP complete problems with polynomial time. The recent advances and principle of DNA computer are introduced. The future development and the bioinformatical significance of DNA computer are also analyzed and discussed.