To effectively solve the problems of small transient bandwidth, serious aperture effect, and high power consumption of phased array radar/antenna, an RF MEMS switch was introduced into the true-time adjustable delay structure, and an adjustable true-time delayer based on the RF MEMS switch was designed. The delay paths with different electrical lengths were selected by MEMS double-throw switches to achieve 5-bit RF signal delay in DC~20 GHz. The geometric parameters of the delay unit were simulated and optimized by using HFSS three-dimensional electromagnetic simulation software. The delay quantities of five switchable delay states are obtained, which are 28.34 ps, 64.76 ps, 101.46 ps, 137.97 ps, 174.61 ps, and 210.98 ps, respectively. The delay step is 36.5 ps, and the overall area is about 5 mm3. Compared with other true-time adjustable delayers, the proposed true-time adjustable delayers has the advantages of multiple controllable bits, a considerable delay bandwidth product and high integration.