<p>Electron transport characteristics through a triple-quantum-dot ring have been investigated theoretically. Using the nonequilibrium Green’s function method, the conductance and current are numerically analyzed. An anti-resonance point always appears in the conductance spectrum and its position can be controlled by tuning the interdot coupling strength. The current is nonzero as a forward bias is applied to the system, while the current becomes zero as a small reverse bias is applied. This characteristic enables the system to be used as a diode. The current becomes spin-dependent as a Zeeman magnetic field is considered. A 100% polarization and -100% polarization can be realized by controlling the Zeeman magnetic field intensity, suggesting the physical scheme as a spin filter. Moreover, the capability of transition between 100% polarization and unpolarization indicates that the system can be designed as a polarization pulse device. The present work provides theoretical insights into the realization of quantum spin-dependent devices and quantum computation applications.</p>