Nanowire is a kind of nanostructures and it usually has a high aspect ratio. Bolometer having nanowire as its active element is belonged to nanobolometer, compared to the microbolometer usually having thin film active element with area of several to tens square microns. A nanobolometer is expected to have many advantages, such as: very simple structure, small size, low noise, high specific detectivity and short response time. In this work, the optical and thermal properties of platinum nanowire in far infrared wavelengths are studied by using multiphysical finite element numerical calculation tool. Relationship between geometry size of platinum nanowire and its optical and thermal properties are revealed. Due to antenna-resonance electric-field-enhanced effect and small size effect, one absorption peak can be found in optical absorption curve of nanowire. The position of absorption peak is connected with the length of nanowire and the value of absorption peak is mainly impacted by the width and thickness of nanowire. When the aspect ratio is too high, the position of absorption peak will move although length does not be changed. At last, a nanowire based nanobolometer which has great optical and thermal characteristics in the wavelength ranging from 8 μm to 14 μm is designed and simulated. Comparing to the previous reported device using the same structure, thermal performance parameter increases one order of magnitude.