Compared with conventional semiconductors, halide perovskite nanocrystals (NCs) have a unique crystal structure and outstanding optoelectronic properties, offering wide potential for applications in optoelectronic devices such as solar cells, photodetectors, light-emitting diodes, lasers, and displays. Rational technological design is providing vital support for the development of perovskite optoelectronics. Herein, monodisperse all-inorganic halide perovskite nanocrystals with consistent morphology and cubic crystal phase were synthesized employing a modified one-pot hot injection method to independently modulate the stoichiometric ratios of three precursors involving cesium salt, lead source, and halide. In combination with an anion exchange reaction, mixing two kinds of perovskite NCs with different halogens enables a transition from violet emission to green and finally to red emission over the entire visible region. Additionally, optical and electrochemical tests suggested that the as-synthesized halide perovskite NCs are promising for photoelectric catalysis applications.