The n-type diamond has been shown to be very difficultly synthesized by CVD method. Nitrogen as a donor impurity shows a similar atom size of carbon for diamond lattice. However, nitrogen doped diamond reveals deep level and large carrier activation energy with much defects in diamond. The application of n-type diamond has less reported and the characteristic of nitrogen doped diamond seems varied due to different fabrication process. Our previous study of nitrogen doped diamond using mixture of N2 and argon gas synthesized by microwave CVD indicated that nitrogen atoms were precipitated in the grain boundaries of diamond crystallites. In this paper, it compared the synthesis of nitrogen doped diamond using the mixed gas of nitrogen/CH4/Ar and ammonia/CH4/Ar gases by microwave CVD method for different temperature, gas flow rate, pressure, and microwave power. The conductivities, carrier concentrations and mobility of the n-type doped diamond have been analyzed and discussed. The Hall measurement shows that the mixture of gas with Ar reveals different growth mechanism and carrier transportation properties in diamond. Nitrogen atoms of N2 were located in the grain boundaries and interfaces among diamond crystallites with the sp2 structure. Nitrogen atoms of NH3 are doped into the diamond crystallites.