The impact of the sensitive parameter of the delay time between pre- and main-current pulse on emission of Ne-like Ar 46.9 nm soft-X-ray laser in capillary discharge at low Ar pressure was investigated. The results indicate that, for ceramic capillary channel with 20 cm in length (4 cm long electrode) and 3 mm in diameter, when the main current pulse spike and Ar pressure were stabilized at 20～21 kA and 38 Pa respectively, the delay time τ of lasing locates in the range of 2.5～12.5 μs which included the optimal smaller range of 3.5～8.5 μs with relatively larger emissions. And at delay time of 5.8 μs there is the biggest laser output. Furthermore, the delay time with the maximum laser output increases gradually with Ar pressure. More detailed experiment afterwards proves that a definite Ar pressure gives out its own delay time range which generates neglectable difference with nearby delay time ranges.