Report variables can be assigned from code before rendering — for values that come from the application rather than the data.

Get a variable and set its value.
var report = new Stimulsoft.Report.StiReport();
report.loadFile("../reports/ReportWithVariable.mrt");

var variable = report.dictionary.variables.getByName("Variable1");
variable.value = "test";

report.renderAsync(function () { /* report is built */ });

How it works. Values are set on the report object prior to rendering, so the output reflects data supplied by the page code.
На скриншоте ниже Вы можете увидеть результат выполнения данного кода:

Setting the Variable Value from Code