Plasma gratings are important in physics because they do not break down in strong fields. Using particle-in-cell (PIC) simulations, a new mechanism to generate plasma grating was developed based on the interactions between picosecond intense laser pulses (the magnitude of $ I $ is ${10}^{15}\;\mathrm{W}/{\mathrm{c}\mathrm{m}}^{2}$ ) and overcritical solid-density plasma (particle number density $n \approx 10{n}_{\rm{c}}$ ). This plasma grating results from the interference of plasma waves excited by strong laser fields in solids. Hence, one laser beam is sufficient for generating the gratings. The method produced a nanometer spatial period, which is significantly different from the micrometer spatial period produced by traditional methods that use two counter-propagating lasers in gas-density plasma. This finding may be useful for manipulating strong x-band frequency laser fields.