ABSTRACT: Based on Dirac negative energy, Einstein mass-energy relation and principle of equivalence, we propose the negative matter as the simplest model of unified dark matter and dark energy. All theories are known, only mass includes positive and negative. Because there is repulsion between positive matter and negative matter, so which is invisible dark matter, and repulsion as dark energy. It may explain many phenomena of dark matter and dark energy. We derive that the rotational velocity of galaxy is approximate constant, and an evolutional ratio between total matter and usual matter from 1 to present 11.82 or 7.88. We calculate the accelerated expansion at 9.76 billion years. Further, the mechanism of inflation is origin of positive-negative matters created from nothing, whose expansion is exponential due to strong interactions at small microscopic scales. We propose specifically some possible ways on observe dark matter in the Milky Way. Many observatories should be able to observe these results. Two evolutional processes from inflation to the matter-dominated universe produce the positive-negative matters, and opposite matters, respectively. Such we may propose a mechanism of missing antimatter when the attraction of the positive and negative charge is greater than the repulsion of positive and negative masses. The negative matter as a candidate of unified dark matter and dark energy is not only the simplest, and is calculable, observable and testable, and may be changed and developed.