In present study, quartz fiber reinforced vinyl-contained polysilazane (Vi-PSN) composite has been fabricated with a resin-like method. Elementary studies on the Vi-PSN matrix show that the polymer is crosslinking at 160 ℃ by adding dicumyl peroxide (DCP). Thermal treatment (280-420℃) after crosslink enhances the thermal stability due to the formation of three dimensional structures through transamination reaction. The composites as prepared at 220℃ and thermal treatment between 280 and 420℃ possess flexural strength of 180-55 Mpa and true density of 1.79-2.12g/cm-3. The flexural strength decreases with the increase of thermal-treatment temperature. Combining thermal properties and mechanical strength data, dielectric properties of composite as prepared and thermal-treated at 380℃ (S380) are compared. The results show the thermal and dielectric properties of S380 keeping with good mechanical properties are significantly improved: decomposition temperature up to 592℃ with dielectric constant of 3.1-3.2 and dielectric loss of 0.0010-0.0022.