Based on the fractal theory, analysis has been made on the size distribution of urban system in Shaanxi Province. Conclusions have been drawn by caculating dimensions of urban system over the past 20 years in Shaanxi province:That the majority of population aggregate in the primate city lead the primacy-rate too high and medium-place city are chasm. This distribution seriously affects exerting of radiating action of the primate city. Based on this analysis, we bring forward that enforcing second-degree city, perfecting traffic and communication system can accelerate exerting of radiating action of the central city.